issue 8, 2013 journal of civil engineering and architecture

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Journal of Civil Engineering and Architecture

Volume 7, Number 8, August 2013 (Serial Number 69)

Contents Construction Materials Research

907 Freezing and Thawing Durability of Ultra High Strength Concrete

Jesus Muro-Villanueva, Craig M. Newtson, Brad D. Weldon, David V. Jauregui and Srinivas Allena

916 Enhancing the Mechanical Properties of Gap Graded Cold Asphalt Containing Cement Utilising

By-Product Material

Abbas Al-Hdabi, Hassan Al Nageim, Felecite Ruddock and Linda Seton

922 Deterioration of Concrete by the Oxidation of Sulphide Minerals in the Aggregate

Jose Duchesne and Benot Fournier

932 Behavior of Millstone Masonry Vaults Strengthened by Composite Materials

Maamoun Saade, Stephan Kesteloot, Chafika Djelal, Lotfi Hamitouche and Idriss Benslimane

940 Corrosion Study and Passive Film Characterization of 11% Cr F/M and 15% Cr ODS Steels

Masatoshi Sakairi, Sublime Ningshen, Keita Suzuki and Shigeharu Ukai

Traffic and Transportation

956 Effect of Traffic Speed on Stresses and Strains in Asphalt Perpetual Pavement

Daba S. Gedafa, Mustaque Hossain and Stefan A. Romanoschi

964 Stresses Analysis on a Rail Part

Cassio Eduardo Lima de Paiva, Jos Luz Antunes de Oliveira e Sousa, Luiz Carlos de Almeida, Paulo

Roberto Aguiar, Luiz Fernando de Melo Correia, Juliana Silva Watanabe, Rodrigo Moreira de Carvalho, Creso de Franco Peixoto and Denis Palomo Paschoalin

973 Advanced Methods of Evaluating Benefits from Improved Flood Immunity in Queensland

Wayne Davies

Earthquake Engineering

992 Policy Analysis on Building Regulations and the Recovery of Earthquake and Tsunami Affected

Areas

Shoichi Ando

1006 Time Dependent Gaussian Equivalent Linearization of Duffing Oscillator Using Continuous

Wavelet Transform

Arunasis Chakraborty, Prateek Mittal and Sabarethinam Kameshwar

1018 An Earthquake Catalogue for El Salvador and Neighboring Central American Countries

(1528-2009) and Its Implication in the Seismic Hazard Assessment

Walter Salazar, Lyndon Brown, Walter Hernndez and Jos Guerra

Aug. 2013, Volume 7, No. 8 (Serial No. 69), pp. 907-915 Journal of Civil Engineering and Architecture, ISSN 1934-7359, USA

Freezing and Thawing Durability of Ultra High Strength

Concrete

Jesus Muro-Villanueva1, Craig M. Newtson1, Brad D. Weldon1, David V. Jauregui1 and Srinivas Allena2 1. Civil Engineering Department, New Mexico State University, Las Cruces NM 88003, USA

2. Civil and Environmental Engineering Department, Washington State University, Richland WA 99354, USA Abstract: Resistance to freezing and thawing of two UHSC (ultra high strength concrete) mixtures was evaluated in accordance with ASTM C 666 Procedure A. The two mixtures (plain and fiber reinforced) were developed using materials local to southern New Mexico, USA. Three different curing regimens were investigated for the mixture with fibers and one curing regimen was studied for the mixture without fibers. All curing regimens included 24 h of ambient curing followed by four days of wet curing at 50 oC, and then two days dry curing at 200 oC. At an age of seven days, one batch of fiber reinforced specimens was air cured at ambient conditions for the following six days and then placed in a water bath at 4.4 oC for 24 h prior to initiating freezing and thawing cycles. The second batch was air cured from day seven to day 12, and then wet cured for one day at 23 oC prior to being placed in the 4.4 oC water bath. The final batch was wet cured at 23 oC from the seventh day to an age of 13 days and then placed in the 4.4 oC water bath. The mixture with no fibers was air cured from the seventh day to an age of 12 days and then wet cured for one day at 23 oC prior to being placed in the 4.4 oC water bath. Higher moisture levels during curing produced greater initial dynamic elastic modulus values and durability factors at the end of the freezing and thawing tests, with the greatest durability factor being 87.5. Steel fibers were observed to improve both compressive strength and durability factor for UHSC. Key words: Ultra high strength, freezing and thawing, durability, dynamic elastic modulus, quality factor.

1. Introduction

UHSC (ultra high strength concrete) is an advanced fiber reinforced composite material, characterized by compressive strengths greater than 140 MPa and flexural strengths greater than 10 MPa at 28 days [1]. UHSC is produced with a high cementitious materials content and a water-to-cementitious materials ratio (w/cm) that is typically less than 0.25. Additionally, the use of silica fume and HRWRA (high range water reducing admixtures) along with pre-setting pressure and post-setting heat treatments have been used to produce high density concrete [1, 2]. A dense microstructure results in very high compressive strengths, including values greater than 200 MPa [3]. Along with the increase in strength, UHSC mixtures

Corresponding author: Craig M. Newtson, Ph.D., research

fields: concrete materials, reuse/recycling of materials, concrete shrinkage, concrete durability, ultra-high performance concrete and nondestructive evaluation of concrete. E-mail: [email protected].

may need to exhibit greater durability to justify the high cost of the material. However, since UHSC is not air-entrained, its ability to withstand cycles of freezing and thawing is questionable and should be investigated.

This paper presents results from freezing and thawing tests conducted on two UHSC mixtures to ensure that UHSC without air entrainment would prove to be durable. The mixtures used in this study were developed by Allena and Newtson [1] using materials local to southern New Mexico, USA. Use of local materials is an improvement in the sustainability of UHSC over pre-packaged, commercially available UHSC products because they offer substantial cost savings. However, the chemical and physical requirements for local materials are not as strict as for commercial products. Additionally, no air-entraining admixture is used in the UHSC mixtures. Consequently, it is even more important to assess the durability of UHSC produced with local materials to

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Freezing and Thawing Durability of Ultra High Strength Concrete

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determine whether or not it is adequate.

2. Background

2.1 ASTM C 666 Procedure A

ASTM C 666 assesses concrete resistance to freezing and thawing by subjecting concrete specimens to rapid repeated freezing and thawing cycles under laboratory conditions. The specimens are molded beams that are cured for 14 days prior to testing. On the last day of curing, the specimens are subjected to a 24 h conditioning period in a 4.4 oC water bath. After the conditioning period, the specimens are subjected to freezing and thawing cycles that are approximately 4 h in duration.

At intervals not to exceed 36 cycles, the specimens are removed from the freezing chamber during the thawed portion of the cycle for dynamic elastic modulus testing. Fundamental transverse frequency (used to compute dynamic elastic modulus), length and mass are measured. Testing of the specimens continues until each of the beams has been subjected to at least 300 cycles of freezing and thawing, or until the dynamic modulus of elasticity decreases to 60% of its initial value or less.

2.2 Dynamic Elastic Modulus

Testing procedures for determining dynamic elastic modulus are specified in ASTM C 215. To determine the dynamic elastic modulus, concrete prisms are excited over a wide range of frequencies using an impact hammer or a transducer to identify the frequency at which the maximum amplitude occurs. The frequency at which the maximum amplitude occurs is the resonant frequency. The concrete specimen is generally assumed to be a single-degree-of-freedom system, for which the resonant frequency is referred to as the fundamental frequency. The fundamental frequency is used to compute dynamic elastic modulus, ED, with the following equation:

2rD CmE (1)

where, C is a constant that accounts for Poissons ratio and the geometry of the specimen, m is the mass of the specimen and r is the measured fundamental frequency.

When ASTM C 215 is used to monitor deteriorating concrete, it is common to present results in terms of the relative dynamic modulus, computed as follows:

)100(o

n

EERDM (2)

where, RDM is the relative dynamic modulus after n cycles of freezing and thawing, En is the dynamic elastic modulus after n cycles, and Eo is the dynamic elastic modulus at zero cycles of freezing and thawing. After completion of freezing and thawing cycles, a durability factor, DF, can be computed as:

MNRDMDF (3)

where, N is the number of cycles imposed, and M is the specified number of cycles (usually 300).

2.3 Quality Factor

When concrete is subjected to cycles of freezing and thawing, degradation can be caused by distributed microcracking in the concrete [4]. This microcracking results in increased damping in addition to a decrease in dynamic elastic modulus. Damping can be quantified by the quality factor, Q, which can be determined from a frequency response curve. An example of a frequency response curve is plotted in Fig. 1. Since a wide range of frequencies are excited by the impact method, amplitudes at frequencies other than the fundamental frequency are known. This allows the quality factor, to be computed with the following relationship:

12

rQ (4)

where, 1 and 2 are the frequencies on either side of r with amplitudes equal to 70.7% of the amplitude of r (Fig. 1). Quality factor is inversely proportional to the damping ratio, , as shown in the following equation:

21Q (5)


909

Fig. 1 Frequency response curve.

Relative quality factor, calculated with an expression similar to Eq. (2), has been shown to be useful for describing deterioration caused by freezing and thawing [4, 5].

2.4 Ultra High Strength Concrete

Shaheen et al. [6] conducted a study on UHSC mixtures with seven day compressive strengths up to 500 MPa. The mixtures included different carbon fibers contents, presetting pressures, curing processes and heat-treating temperatures. Results from ASTM C 666 Procedure A testing revealed that UHSC mixtures with carbon fibers had durability factors of 100, which represents no decrease in dynamic elastic modulus after testing. Conversely, mixtures without fibers tended to show a decrease in dynamic elastic modulus [6].

Other freezing and thawing studies [7, 8] have used various temperature ranges, specimen dimensions and cycle durations. Results showed relative dynamic modulus of 100 after up to 800 cycles of freezing and thawing. The percentage of mass lost during testing on both studies was extremely low or zero. It was concluded that the UHSC mixture provided excellent frost resistance.

Graybeal [9] presented results from ASTM C 666 Procedure A testing that showed that various steam curing regimens as well as duration of exposure to each treatment greatly influence UHSC durability

factors. Mixtures exposed to longer wet curing regimens produced greater initial dynamic elastic modulus, but tended to produce lower durability factors.

Studies on curing of high performance concrete mixtures have shown that the microstructure of the surface concrete can be disturbed by the curing method, resulting in a reduction in durability [10]. High performance concrete mixtures with silica fume are more sensitive to curing methods than mixtures without silica fume due to microcracking caused by desiccation [10]. Hasni et al. [10] presented results that show that high performance concrete mixtures with high silica fume contents have less microcracking when cured at a higher relative humidity.

Non air-entrained concrete mixtures along with low water to binder ratios may have satisfactory durability against freezing and thawing if a compressive strength of at least 24 MPa is achieved prior to the first freezing cycle [10]. The use of a low water to binder ratio ensures that all of the mixing water combines with the cementitious material, resulting in a concrete with low permeability that prevents critical saturation of the paste. Therefore, the presence of an air void system in the concrete is not essential [11].

3. Experimental Methods

The two UHSC mixtures used in this study were developed by Allena and Newtson [1]. Compressive strengths obtained from 51 mm cubes at 28 days were 170.3 MPa for the fiber reinforced UHSC mixture and 159.9 MPa for the plain UHSC mixture.

3.1 Materials

Type I-II portland cement, silica fume and local alluvial sand from Las Cruces, New Mexico, USA were used to produce the UHSC mixtures in this research. Steel fibers with a length of 13 mm were used to improve ductility. Workability was obtained using a polycarboxylate-based HRWRA (Glenium

Frequency

Am

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1.00.707

r 2


910

3030 NS from BASF). The local sand had a specific gravity of 2.53 and an

absorption of 1.2%. Table 1 presents the grain size distribution of the sand. The sand was sieved to retain particles between ASTM #30 and #200 (600 m and 75 m) sieves. The sand was first passed through a No. 30 (600 m) sieve and then washed over a No. 200 (75 m) sieve. The sand was then oven dried and placed in an air tight container to ensure 0% moisture content.

3.2 Concrete Mixtures

Two different concrete mixtures (with and without fibers) were tested for freezing and thawing resistance according to ASTM C 666 and for compressive strength according to BS 1881. Saturated surface-dry mixture proportions for both mixtures are presented in Table 2.

3.3 Mixing and Curing

The dry constituents of each mixture were mixed for 15 min using a 20 L pan mixer. Then, 75% of the water was added and mixing continued for 5 min. The HRWRA was then added, and mixing continued for another 5 min. Next the remaining 25% of the water was added and mixing continued for another 10 min. The final step in the mixing process was to add the steel fibers and mix for another 5 min.

Slump measurements were performed for both UHSC mixtures in accordance with ASTM C 143. The fiber reinforced UHSC mixture produced a slump of 235 mm while the plain UHSC mixture had a slump of 180 mm.

Freezing and thawing specimens were prepared according to ASTM C 192. Each prism was prepared in two layers. Consolidation was achieved by rodding

each layer every 1,400 mm2 of the surface using a 16 mm rod. After specimens were rodded, they were externally vibrated using a table vibrator to improve consolidation. Theoretical densities for the UHSC mixtures were 2,286 kg/m3 for fiber reinforced UHSC and 2,205 kg/m3 for plain UHSC. Density of the hardened UHSC was measured at 24 h and was found to be 2,343 kg/m3 for fiber reinforced UHSC and 2,261 kg/m3 for plain UHSC. These values were increases of 2.49% and 2.55% from the theoretical density for the fiber reinforced and plain UHSC mixtures, respectively.

A total of four 76 mm 102 mm 406 mm prisms were produced from each batch for ASTM C 666 testing. The fiber reinforced UHSC mixture was used to produce a total of 12 prisms (three batches) while the plain UHSC mixture was used to produce four prisms. In addition to the prisms, four 102 mm and eight 51 mm cubes were prepared from each batch for compressive strength testing at 14 days.

The specimens were cured for 14 days prior to testing. During the first seven days, the curing regimen was the same for all of the batches. The specimens remained in their molds for 24 h at room temperature 25 oC. After demolding, the specimens were heat cured in a waterbath at 50 oC for the following four days. Then, they were dry cured in an oven at 200 oC for two days. Curing at these elevated temperatures to an age of seven days was necessary to achieve the desired strength.

Table 1 Grain size distribution of sand. Sieve No. Sieve size (m) Passing (%) 30 600 100.0 50 300 31.7

100 150 2.9 200 75 0.0

Table 2 Saturated surface-dry mixture proportions of UHSC mixtures.

Mixture Cement (kg/m3) Silica fume (kg/m3)

Fine sand (kg/m3)

Steel fibers (kg/m3)

Water (kg/m3)

HRWRA (l/m3) w/c w/cm

Fiber reinforced 890 222 799 119 222 29.6 0.25 0.20 Plain 890 222 837 - 222 29.6 0.25 0.20


911

From an age of seven days to an age of 14 days, three different curing regimens were investigated to identify practices that might improve UHSC durability. The three curing regimens that seemed most likely to be used in practice were:

Regimen 1: Specimens were air cured for six days at room temperature, 25 oC, followed by 24 h of conditioning in a water bath at 4.4 oC;

Regimen 2: Specimens were air cured for five days at 25 oC, followed by one day of moist curing at 23 oC, and then 24 h conditioning in a water bath at 4.4 oC;

Regimen 3: Specimens were moist cured for six days at 23 oC, followed by 24 h of conditioning in a water bath at 4.4 oC.

Regimens 1 through 3 were used on the fiber reinforced mixture, but only regimen 2 was used for the plain UHSC mixture.

3.4 Testing Program

Cube specimens were tested for compressive strength at 14 days according to BS 1881. Prism specimens were tested for resistance to freezing and thawing according to ASTM C 666 Procedure A. In accordance with this testing method, a 3-h 31-min cycle was selected. One full cycle of freezing and thawing consisted of rapid temperature decrease from 4.4 oC to -17.8 oC in approximately 2 h 20 min. The temperature was then held constant for 8 min before raising the temperature back to 4.4 oC in 53 min. The temperature was then held constant at 4.4 oC for 10 min. Testing was conducted during this 10 min window.

The specimens were subjected to 300 cycles of

freezing and thawing (or less when the relative dynamic elastic modulus of a specimen dropped below 60). Length, mass and fundamental frequency (to compute dynamic elastic modulus) measurements were taken at intervals no greater than 36 cycles. Distilled water was used in the conditioning water bath and for immersion of the specimens during freezing and thawing cycles.

4. Results and Discussion

4.1 Compressive Strength

Compressive strengths at 14 days for the fiber reinforced and plain UHSC mixtures are presented in Table 3. These values are less than the 28 day strengths (170.3 MPa for fiber reinforced UHSC and 159.9 MPa for plain UHSC) reported by Allena and Newtson [1] because testing was conducted at 14 days. Fiber reinforced UHSC mixtures produced greater 14 day strengths than the plain UHSC mixture for batches cured under the same regimen. The increase in compressive strength caused by the fibers was approximately 11% for 51 mm cubes and 17% for 102 mm cubes. It was observed that batches with wetter curing regimens between ages of seven and 14 days did not produce greater strength.

4.2 Freezing and Thawing

Initial dynamic elastic modulus results are also presented in Table 3. Mixtures exposed to longer periods of wet curing produced greater initial dynamic elastic modulus values than mixtures with drier curing regimens. Curing regimen 3 produced a 25% greater initial dynamic elastic modulus than curing regimen 1

Table 3 Average compressive strength and initial dynamic elastic modulus values.

Mixture Curing regimen Compressive strength (MPa) Initial dynamic elastic

modulus (GPa) 102 mm cubes 51 mm cubes Fiber reinforced 1 130.2 141.1 32.4 2 136.0 146.6 34.8 3 132.8 137.1 40.8 Plain 2 123.0 124.9 34.4


912

for the fiber reinforced UHSC. Fiber content did not appear to influence initial values of dynamic elastic modulus since the fiber reinforced and plain UHSC mixtures had similar values when curing regimen 2 was used.

Figs. 2-4 show the relative dynamic modulus values versus cycles of freezing and thawing for individual specimens from each of the three curing regimens for the fiber reinforced UHSC mixture. Results show a consistent decline in relative dynamic modulus throughout the duration of the testing. However, specimens with drier curing regimens experienced a more rapid decline in relative dynamic modulus than specimens with wetter curing regimens. Wetter curing regimens also seemed to produce less variation between the relative dynamic modulus of specimens within the same group.

Fig. 5 presents relative dynamic modulus values versus cycles of freezing and thawing for the plain UHSC mixture. This mixture was only tested under curing regimen 2. The initial dynamic elastic modulus values for this mixture were nearly the same as those from the fiber reinforced UHSC mixture cured under regimen 2. However, relative dynamic modulus of the plain UHSC mixture declined more abruptly than the relative dynamic modulus of the fiber reinforced specimens cured according to regimen 2. Average values for each of the four mixture and curing regimen combinations investigated in this study are provided in Fig. 6. As observed in Figs. 2-5, relative dynamic modulus declined more rapidly for drier curing regimens, as well as in the mixture without steel fibers. This behavior is consistent with observations by Graybeal [9] on specimens with wet versus dry curing regimens.

The fiber reinforced mixture with curing regimen 1 reached an average relative dynamic modulus of 60 at cycle 196. According to ASTM C 666 it is considered to have failed. The average relative dynamic modulus of the remaining mixtures did not drop below 60 before completing the testing period.

For the plain and fiber reinforced specimens cured according to regimen 2, degradation of the plain mixture occurred more rapidly than in the fiber reinforced mixture. It was observed that the use of steel fibers not only provided greater compressive

Fig. 2 Relative dynamic modulus for fiber reinforced UHSC cured according to regimen 1.



0

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0 50 100 150 200 250 300Cycles

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Fig. 5 Relative dynamic elastic modulus for plain UHSC cured according to regimen 2.

Fig. 6 Average relative dynamic modulus for all batches.

strength, but also improved the resistance to freezing and thawing by restraining the expansion of the microcracks.

Fig. 7 presents the average relative quality factor values versus cycles of freezing and thawing for the four combinations of mixtures and curing regimens. It was observed that the relative quality factor dropped below 60 within 20 to 50 cycles for all of the combinations.

As with decreases in relative dynamic modulus, decreases in relative quality factor were more rapid for specimens with drier curing regimens and for the mixture without steel fibers. The most abrupt decline in quality factor was observed for specimens subjected to curing regimen 1. This abrupt decline coincided with an early failure (based on relative dynamic modulus) of the specimens cured using that regimen.

Table 4 presents a summary of the average durability factors for the four combinations of mixtures and curing regimens. The durability factors represent the relative dynamic modulus values at the end of the freezing and thawing cycles (Fig. 6). Durability factors were greater for wetter curing regimens. Curing regimen 3 produced the greatest durability factor (87.5). Although only four specimens were tested for each batch, all of the average durability factors were significantly different (95% confidence) except the plain mixture and the fiber reinforced mixture cured under regimen 1.

Minor scaling occurred at approximately 100 cycles for all specimens, whereas spalling of corners only occurred on the fiber reinforced UHSC mixture with curing regimen 1 and on the plain UHSC mixture. Elongation of prisms was relatively constant throughout the duration of testing. Elongation values at the end of testing ranged from 0.18% to 0.22%.

Mass of the freezing and thawing specimens increased as water filled microcracks caused by freezing and thawing. Fig. 8 shows the average relative mass change for the specimens.

Fig. 7 Average relative quality factor for all batches.

Table 4 Average durability factors.

Mixture Curing regimen Durability factor Fiber reinforced 1 39.7 2 72.6 3 87.5 Plain 2 55.1

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Fiber reinforced mixture, Regimen 1Fiber reinforced mixture, Regimen 2Fiber reinforced mixture, Regimen 3Plain mixture, Regimen 2

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Fig. 8 Relative mass for all batches.

The wettest curing regimen (regimen 3) resulted in substantially less mass gain than the drier curing regimens.

4.3 Modulus of Rupture

Modulus of rupture for the UHSC mixtures was determined using ASTM C 78 testing procedures. This test was performed using a simple beam with third-point loading.

Allena and Newtson [1] reported the seven day modulus of rupture strengths of undamaged specimens (76 mm 102 mm 406 mm) to be 17.5 MPa for fiber reinforced UHSC and 10.9 MPa for plain UHSC. At the end of freezing and thawing cycles conducted in the present work, the deteriorated test specimens were tested for modulus of rupture. Results from this testing are presented in Table 5. All of the specimens lost at least 60% of the 7-day flexural strength. The fiber reinforced mixture cured according to regimen 2 provided greater flexural strength after completion of 300 cycles of freezing and thawing than the plain UHSC mixture. However, the percentage decrease in modulus of rupture from the 7-day strengths given in Allena and Newtson [1] were comparable for the plain and fiber reinforced UHSC specimens cured according to regimen 2. Specimens exposed to wetter curing conditions also retained greater modulus of rupture values.

Greater durability factors corresponded to greater modulus of rupture values at the end of testing for results

Table 5 Modulus of rupture results after ASTM C 666 testing.

Mixture Curing regimen Modulus of rupture (MPa)

Percent of 7-day strength

Fiber 1 3.75 21.4 Reinforced 2 5.18 29.6 3 5.90 33.7 Plain 2 2.61 23.9

Fig. 9 Percentage of 7-day flexural strength versus durability factor for fiber reinforced UHSC mixtures.

obtained within the fiber reinforced UHSC mixture. Fig. 9 illustrates the correlation between durability factor and retained modulus of rupture percentage, showing that the relationship is nearly linear.

5. Conclusions

The effects of the different curing methods on compressive strength were observed to be negligible. Conversely, initial dynamic elastic modulus values for concrete specimens with wetter curing conditions were greater than those from specimens with drier curing conditions. The presence of fibers did not appear to influence initial dynamic elastic modulus.

Providing more moisture in the last seven days of curing following the heat treatment increased the durability of UHSC. It was observed that any increase in curing moisture resulted in improved durability factors. Wetter curing also resulted in less mass gain during ASTM C 666 testing, greater modulus of rupture at the end of the freezing and thawing cycles, and less variation in relative dynamic modulus between specimens from the same group. Durability

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of UHSC exposed to freezing and thawing was also improved by the use of steel fibers.

Quality factors decreased sharply almost immediately after freezing and thawing cycles were initiated for all specimens. The quality factors produced the same trends observed for relative dynamic modulus but served as an earlier indicator of deterioration. However, it is difficult to provide a good correlation between quality factor and relative dynamic modulus degradation because the decline in quality factor was so rapid.

Modulus of rupture decreased more than relative dynamic modulus. In fact, even when durability factor was acceptable (greater than 60) modulus of rupture still decreased by more than 60% from the seven day strength values.

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mixtures using local materials, in: International Concrete Sustainability Conference, National Ready Mixed Concrete Association, Tempe, AZ, Apr. 2010, http://www.concretetechnologyforum.org/2010CSCProceedings (accessed July 9, 2011).

[2] J.C. Scheydt, H.S. Mller, Microstructure of ultra high performance concrete (UHPC) and its impact on durability, in: The 3rd International Symposium on UHPC and Nanotechnology for High Performance Construction Materials, Kassel, Germany, 2012, pp. 349-356.

[3] M. Cheyrezy, P. Richard, Composition of reactive powder concrete, Cement and Concrete Research 25 (7) (1995)

1501-1511. [4] E. Vokes, S. Clarke, E. Janssen, Damping measurements

for nondestructive evaluation of concrete beams, in: Proceedings of International RILEM Workshop on Resistance of Concrete to Freezing and Thawing with or Without Deicing Chemicals, UK, 1997, pp. 1-10.

[5] J. Muro-Villanueva, C.M. Newtson, B.D. Weldon, D.V. Jauregui, S. Allena, Freezing and thawing durability of ultra high strength concrete, in: International Congress on Durability of Concrete, Trondheim, Norway, 2012.

[6] E. Shaheen, N.J. Shrive, Optimization of mechanical properties and durability of reactive powder concrete, ACI Materials Journal 103 (6) (2006) 444-451.

[7] W.Y. Ji, M.Z. An, G.P. Yan, J.M. Wang, Study on Reactive Powder Concrete Used in Sidewalk System of the Qinghai-Tibet Railway Bridge, 2007, http://www.cptechcenter.org/publications/sustainable/jireactive.pdf (accessed July 11, 2011).

[8] J. Pirard, B. Dooms, N. Cauberg, Evaluation of durability parameters of UHPC using accelerated lab tests, in: The 3rd International Symposium on UHPC and Nanotechnology for High Performance Construction Materials, Kassel, Germany, 2012, pp. 371-376.

[9] B. Graybeal, Material Property Characterization of Ultra-High Performance Concrete, Federal Highway Administration report No. FHWA-HRT-06-103, McLean, VA, 2006.

[10] L. Hasni, J.L. Gallias, M. Salomon, Influence of the curing method on the durability of high performance concretes, durability of concrete, in: Third International Conference, Nice, France, 1994, pp. 131-155.

[11] B. Mather, How to make concrete that will be immune to the effects of freezing and thawing, International Concrete Research & Information Portal 122 (1990) 1-18.


Enhancing the Mechanical Properties of Gap Graded

Cold Asphalt Containing Cement Utilising By-Product

Material

Abbas Al-Hdabi1, 2, Hassan Al Nageim1, Felecite Ruddock1 and Linda Seton3 1. School of Built Environment, Liverpool John Moores University, Liverpool L3 2ET, UK

2. Engineering Faculty, Kufa University, Alnajaf 54001, Iraq

3. School of Pharmacy and Bimolecular Science, Liverpool John Moores University, Liverpool L3 3AF, UK

Abstract: The little stiffness modulus, high voidage and long curing time has limited the use of CBEMs (cold bituminous emulsion mixtures) in road and highways to pavement experiencing low traffic. The aim of this study is to improve the properties of gap graded CRA (cold rolled asphalt) containing OPC (ordinary portland cement) as filler by addition of a by-product material as an activator. OPC was added to the CRA as a replacement to the conventional mineral filler (0%-100%), while LJMUA (Liverpool John Moores University Activator) was added as an additive in the range from 0%-3% by total mass of aggregate. Laboratory tests included stiffness modulus and uniaxial creep test to assess the mechanical properties. The results have shown a considerable improvement in the mechanical properties from the addition of LJMUA to the CRA containing OPC especially for the early life stiffness modulus that is the main disadvantage of the cold mixtures. Key words: Stiffness modulus, creep stiffness, ordinary portland cement, cold rolled asphalt.

1. Introduction

HRA (hot rolled asphalt) surface course is a continuous gap graded mixture of mineral filler, sand and bitumen coarse aggregate is added to it. The mechanical properties of the mixture are controlled by the strength properties of the mortar, i.e., mineral filler, sand and bitumen. The material is widely used for surfacing major roads in UK because it provides a dense, impervious layer resulting in a weather resistant and durable surface able to withstand the demands of todays traffic loads, providing good resistance to fatigue cracking. Nevertheless, it might experience some weakness to deformation resistance [1].

Additionally, the use of CBEMs (cold bituminous emulsion mixtures) for road construction,

Corresponding author: Abbas Al-Hdabi, Ph.D. student,

lecturer, research fields: roads materials and sustainable asphalt technologies. E-mail: [email protected].

rehabilitation and maintenance is gaining interest day by day, as these mixtures offer advantages over traditional hot mixtures in different terms such as, environmental impact, energy saving, cost effectiveness, safety and cheap production processes. In UK, todays use of cold mix takes less interest compared with HMA (hot mix asphalt), as this mixtures show low earlier strength to resist the different traffic loads and low resistance to water damage especially rainfall. Other countries such as USA, European countries and Australia showed more interest in the uses of the materials due to the above advantages [2].

Chevron Research Company in California after many research studies reported that full curing of cold bituminous mixtures on site depending on the weather conditions and curing times may extend from 2-24 months. Unfortunately, UK weather conditions are not assistant to decrease the curing time, humid, cold and rainy most time of the year [3].

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Several studies have been implemented on improving the mechanical properties of the cold mixes in terms of OPC (ordinary portland cement) addition. Initial study conducted by Head [4] and focused on the improvement on the Marshall Stability of the modified cold asphalt mix. He stated that Marshall Stability of modified cold asphalt mix increased by about three times with the addition of 1% OPC compared with un-treated mix.

Li et al. [5] conducted experiments to assess the mechanical properties of a three-phase CAEC (cement-asphalt emulsion composite). Through experimental study, they showed that CAEC possessed most of the characteristics of both cement and asphalt, namely the longer fatigue life and lower temperature susceptibility of cement concrete, and higher toughness and flexibility of asphalt concrete.

Oruc et al. [6] implemented experiments to assess the mechanical properties of emulsified asphalt mixtures having 0-6% OPC. The test results revealed considerable improvement with high OPC addition percentage. Furthermore, they recommended that the cement modified asphalt emulsion mixes might be used as structural pavement layer.

Another study implemented by Wang and Sha [7] indicated that the rise of cement and mineral filler fineness has a positive impact on micro hardness of the interface of aggregate and cement emulsion mortar. Moreover, they concluded that the limestone and limestone filler impact hardness value are highly when compared with granite and granite filler.

The main aim of this research is to improve the mechanical properties of gap graded CRA (cold rolled asphalt) containing OPC instead of conventional filler by addition of a by-product material. To achieve this aim, LJMUA (Liverpool John Moores University Activator) was used as additive in the range from 0%-3% by total mass of the aggregate to the CRA containing different amounts of OPC. Stiffness modulus and uniaxial compressive cyclic creep tests

were used to assess the mechanical properties in this investigation.

2. Experimental Program

2.1 Materials Properties

The coarse and fine aggregate used in this investigation were crushed granite and their physical properties are shown in Table 1. Two types of filler were used in this study, traditional mineral filler (limestone dust) and OPC, and a high silica (more than 75% SiO2) by-product material with 10 microns average particle size has been used as an additive, i.e., LJMUA. The aggregate was dried, riffled and bagged with sieve analysis achieved in accordance with BS EN 933-1 [8].

The cationic slow setting bituminous emulsion (K3-60) was used to produce the novel CRA to develop high adhesion between aggregate particles. In contrast, a 125-pen and 50-pen bitumen grades were used to produce the traditional HRA. The properties of the selected bituminous emulsion and bituminous binder are shown in Table 2.

2.2 Selected Gradation

The aggregate gradation of wholly mixtures (CRA and HRA mixtures) used in this study was based on BS EN 13108-4 [9] for HRA, 55/14C gap graded surface course mixture gradation has been used in this work. The selected gradation is shown in Table 3.

2.3 Preparation of CRA and HRA Mixtures

The design procedure for the new CRA mixtures used in this investigation was based on the method adopted by the Asphalt Institute (Marshall Method for Emulsified Asphalt Aggregate Cold Mixture Design (MS-14)) [10]. According to this procedure pre-wetting water content, optimum total liquid content at compaction and optimum residual bitumen content were 5%, 15.16% and 7%, respectively.


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Table 1 Physical properties of aggregate.

Material Bulk specific gravity (g/cm3) Apparent specific gravity (g/cm3) Water absorption (%) Coarse aggregate 2.79 2.83 0.6 Fine aggregate 2.68. 2.72 1.6 Mineral filler 2.71 - -

Table 2 Bituminous binder and bitumen emulsion properties.

Bitumen emulsion (K3-60) Bituminous binder (40-60) Bituminous binder (100-150) Property Value Property Value Property Value

Appearance Black to dark brown liquid Appearance Black Appearance Black

Boiling point (C) 100 C Penetration at 25 C 43 Penetration at 25 C 122 Relative density at 15 C (g/ml) 1.05 Softening point (C) 54 Softening point (C) 43.6 Residue by distillation (%) 64 Density at 25 C 1.02 Density at 25 C 1.05

Table 3 Aggregate gradation for 55/14C gap graded surface course (BS EN 13108-4).

Sieve size, mm 20 14 10 2 0.5 0.25 0.063 Percent passing (specification range) 100 98-100 42-63 40 19-31 9-31 6 Percent by mass (passing mid) 100 99 52 40 25 20 6

Different percentages of OPC (0%, 1.5%, 3%, 4.5% and 6% by total mass of aggregate) as a replacement for the conventional mineral filler were used in preparation of the specimens of CRA mixtures. On the other hand, a by-product material (LJMUA) was used as an additive to the CRA mixtures containing OPC with a range of 0%-3% by total mass of aggregate. In contrast, HRA mixture samples were prepared with the same aggregate type and gradation, 5.5% optimum binder content was used according to the BS 594987 Annex H [11] for the 55/14C HRA surface course design mixture. Both cold and hot mixes were prepared to produce three specimens for each specific mix. The cold mix specimens were mixed and compacted at lab temperature, i.e., 20 oC, while 125-pen and 50-pen hot mix specimens were mixed at (150-160 oC) and (160-170 oC), respectively.

2.4 Curing of the CRA Samples

The conditioning of the CRA specimens is depending on the procedure adopted by the Asphalt Institute MS-14 [10]. The curing process involves two stages: The first stage was achieved with 24 h @ 20 oC as the sample needs to be left in the mould before being extruded to prevent specimen disintegration;

while stage two was achieved with 24 h @ 40 oC (the samples have been left in the ventilated oven). After these stages, the samples have been left in the lab (20 oC) and tested at different ages, i.e., 2, 7, 14 and 28 days to indicate the indirect tensile stiffness modulus. This curing process, i.e., 24 h @ 20C plus 24 h @ 40C represents 7-14 days in the field as reported by Jerkins [12].

3. Testing

3.1 ITSM (Indirect Tensile Stiffness Modulus)

The test is conducted at 20 oC in accordance with BS EN 12697-26:2004 [13], Cooper Research Technology HYD 25 apparatus was used (Fig. 1).

3.2 UCCT (Uniaxial Compressive Cyclic Test)

The UCCT is a destructive test used mainly to evaluate the permanent deformation characteristics of hot mixes. UCCT at 40 oC was used to assess the effect of addition of LJMUA to the CRA containing OPC on creep performance. The test was conducted in accordance with BS EN 12697-25 [14], also Cooper Research Technology HYD 25 testing apparatus was used (Fig. 2).


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Fig. 1 HYD 25 indirect tensile apparatus.

Fig. 2 Creep test configuration.

4. Results and Discussion

4.1 ITSM Results

The specimens were tested according to BS EN 12697-26:2004 [13] at ages 2, 7, 14 and 28 days to assess the effect of replacement of conventional mineral filler with OPC as well as the addition of LJMUA to these mixtures, as shown in Figs. 3-5. It is obviously shown that the addition of OPC instead of filler in the CRA increased the stiffness modulus considerably. This enhancement in ITSM results is due to firstly, another binder was generated in addition to the bitumen residue binder produced from the hydration process of the hydraulic reaction of OPC and secondly loss of the trapped free water which is absorbed by OPC.

Also there is incredible enhancement to the stiffness modulus from the addition of LJMUA to the CRA containing OPC within the early life of mixtures. It is clearly shown that addition of 2% LJMUA to the CRA containing 3% OPC increased the stiffness

Fig. 3 Influence of curing time and OPC percentage on SM results.

Fig. 4 Influence of addition of 1% LJMUA to CRA containing OPC after two days.

Fig. 5 Influence of addition of LJMUA to CRA containing 3% OPC after two days.

modulus more than three times and its value is more than the target value for the 125-pen HRA, i.e., 1,941 MPa. This further improvement is due to the degree of hydration of OPC is increased when the high silica ash, i.e., LJMUA were added in the CRA mixtures and was working as an activating agent to OPC. This finding corroborates the ideas of Dillshad [15], who found similar effect by incorporating high silica material in OPC system.

6,000

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0

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0

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Fig. 6 Creep strain versus number of pulse applications of specimens with different percent of OPC.

Fig. 7 Influence of percent of LJMUA on ultimate creep stiffness of CRA containing OPC.

4.2 UCCT Results

Figs. 6 and 7 show the results of the UCCT tests for CRA containing cement with and without LJMUA. The creep strain versus number of pulse applications for CRA containing OPC is shown in Fig. 6, while Fig. 7 displays the effect of addition of 1% LJMUA to the CRA containing 1.5% and 3% OPC on creep stiffness.

These figures reveal the positive effect of OPC on the creep properties of CRA, specimens with 1.5% OPC decrease the creep strain incredibly compared to the control specimens as well as HRA mixtures. On the other hand, there is no ad the addition of LJMUA to the CRA mixtures containing OPC on the creep performance of these ditional outstanding from mixtures.

5. Conclusions

Adding the by-product material LJMUA to the CRA containing OPC as mineral filler provides a promising enhancement to the mechanical properties of the new CRA mixtures (especially stiffness modulus) to a level that they are comparable with those of HRA mixtures.

The main conclusions drawn from this investigation are as follows:

(1) The replacement of the conventional mineral filler with OPC into the CRA mixtures improves significantly the stiffness modulus results especially with higher percentages of filler replacement (4.5% and 6%);

(2) The addition of LJMUA increases considerably the stiffness modulus of the CRA containing OPC. Addition of 1% of LJMUA to the CRA containing 3% OPC improves the stiffness modules more than twice and addition of 2% LJMUA increases it to more than three times (its value is more than the target point for the conventional 125-pen HRA);

(3) The replacement of conventional mineral filler with OPC can also improve the permanent deformation resistance when compared to both control CRA and traditional HRA. The creep stiffness improves more than 6 times for the CRA containing

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just 1.5% OPC compared with the control CRA; (4) There is no further outstanding from the

addition of LJMUA to the CRA containing OPC, i.e., the creep performance for the CRA containing OPC with or without LJMUA is better than the performance of the control CRA as well as HRA prepared with 50-pen and 125-pen bitumen.

References [1] J.C. Nichollas, Asphalt Surfacings, Taylor and Francis

e-Library, London, 2004. [2] I.N.A. Thanaya, Improving the Performance of Cold

Bituminous Emulsion Mixtures (CBEMs) Incorporating Waste Materials, University of Leeds, UK, 2003.

[3] D. Leech, Cold Bituminous Materials for Use in the Structural Layers of Roads in Traspotation Research Laboratory, Project report 75, UK, 1994.

[4] R.W. Head, An informal report of cold mix research using emulsified asphalt as a binder, in: Association of Asphalt Paving Technologists Proceeding (AAPT), USA, 1974.

[5] G. Li, Y. Zhao, S. Pang, W. Huang, Experimental study of cement-asphalt emulsion composite, Cement Concrete Research 28 (5) (1998) 635-641.

[6] S. Oruc, F. Celik, V. Akpinar, Effect of cement on emulsified asphalt mixtures, Journal of Materials Engineering and Performance 16 (5) (2007) 578-583.

[7] Z.S. Wang, A. Sha, Micro hardness of interface

between cement asphalt emulsion mastics and aggregates, Journal of Materials and Structures 43 (2010) 453-461.

[8] Determination of Partical Size Distribution-Sieving Method-Test for Geometrical Properties of Aggregate, British Standard Institution, BS EN 933-Part 1, London, UK, 1997.

[9] Bituminous Mixtures Materials Specification-Hot Rolled Asphalt, British Standard Institution, BS EN 13108: Part 4, London, UK, 2006.

[10] Asphalt Cold Mix Manual, Manual Series No.14 (MS-14), Asphalt Institute, Maryland, USA, 1989.

[11] Asphalt for Roads and Other Paved Areas-Spacefication for Transport, Laying, Compaction and Type Testing Protocols, British Standard Institution, BS 594987, London, UK, 2010.

[12] K. Jerkins, Mix design consedrations for cold and half-warm bitumious mixes with emphasis on foamed asphalt, Doctoral Dissertation, University of Stellenbosch, 2000.

[13] Bitumenous Mixtures-Test Methods for Hot Mix Asphalt-Stiffness, British Standard Institution, BS EN 12697: Part 26, London, UK, 2004.

[14] Bituminous Mixtures Test Methods for Hot Mix AsphaltPart 25: Cyclic Compression Test, British Standard Institution, London, UK, 2005.

[15] D.K.H. Amen, Degree of hydration and strength development of low water-to-cement ratios in silica fume cement system, International Journal of Civil and Environment Engineering 11 (5) (2011) 10-16.


Deterioration of Concrete by the Oxidation of Sulphide

Minerals in the Aggregate

Jose Duchesne and Benot Fournier Department of Geology and Geological Engineering, Universit Laval, Qubec G1Y 2S4, Canada

Abstract: Cases of degradation of concrete associated to iron sulphides in aggregates were recently recognized in the Trois-Rivires area, Canada. The aggregate used to produce concrete was an anorthositic gabbro containing various proportions of pyrite, pyrrhotite, chalcopyrite and pentlandite. Quantitative microanalysis on sulphide minerals show that pyrrhotite contains small amount of Ni, Co, Cu and As substituting for Fe in the mineral structure. Considering element substitution, x value in the chemical formula (Fe1-xS) was calculated to 0.099 in the pyrrhotite studied. Petrographic examination of damaged concretes showed the presence of oxidized pyrrhotite. The observation of polished samples shows, in several cases, that the pyrite is intact while the pyrrhotite presents evident signs of oxidation. In the presence of water and oxygen, pyrrhotite oxidizes to form iron oxyhydroxides and sulphuric acid. The acid then reacts with the phases of the cement paste and provokes the formation of gypsum and ettringite. These minerals were observed by SEM-EDS (scanning electron microscope/energy dispersive x-ray spectrometer) and their precipitation causes a volume increase that creates expansion and cracking of the concrete.

Key words: Sulphide minerals, oxidation, expansion, petrographic examination, concrete durability.

1. Introduction

Over the past few years, rapid deterioration of concrete foundations occurred in a few housing developments in the Trois-Rivires area (Qubec, Canada) two to four years after construction. More than 400 residential owners have faced serious issues related to the deterioration of their concrete foundations and slabs. In some cases, the deterioration was such that immediate remedial actions were required.

The distressed concretes display map cracking on the surface of the walls. A large number of concrete samples were investigated. In all cases, the aggregate material used for the concrete manufacturing was an intrusive igneous rock, more precisely an anorthositic gabbro, containing various proportions of sulphide minerals mostly pyrite (FeS2) and pyrrhotite which is a non-stoichiometric mineral of general formula Fe1-xS, with x varying from 0 to 0.125 [1-3]. A

Corresponding author: Jose Duchesne, Ph.D., professor, research field: concrete durability. E-mail: [email protected].

deleterious process involving the oxidation of sulphide minerals is thought to have caused the swelling and cracking of the affected concrete elements.

This study reports the results of site inspections along with concrete cores characterisation using different petrographic tools including stereomicroscope, polarizing microscope, SEM (scanning electron microscope) and EPMA (electron probe micro-analyser). The goal of that study is to present a detailed characterization of the materials in order to reach a better understanding of the mechanisms involved. The next step will be the establishment of a performance test enabling to reliably screen aggregates that can cause deleterious expansion/cracking due to oxidation in concrete.

2. Materials and Methods

2.1 General

The diagnosis of any concrete deterioration starts with visual site inspection. Visual inspection of

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concrete foundations will include the identification of any evidence of deformation, cracking (pattern and intensity), exposure conditions including water drainage, etc.. Visual inspection also helps selecting sampling locations. Concrete samples (100-mm diameter cores) were drilled through the foundation walls for petrographic examination. Concrete cores were examined for any sign of deterioration and some cores were selected for further testing.

2.2 Materials

Crushed coarse aggregates were sampled directly from selected stockpiles at the St-Boniface quarry North of Trois-Rivieres, Qubec, Canada. Concrete cores were drilled in different housing foundation walls in the Trois-Rivires area. Crushed aggregates were examined as they are and on polished sections. Concrete cores were cut or broken for megascopic and microscopic examinations.

2.3 Methods for Assessment and Analysis

(1) General First, concrete cores were cut with a diamond blade.

Some surfaces were polished for stereomicroscope observations. Selected sub-samples were impregnated under vacuum with low viscosity resin (Epofix resin, Struers) and polished for polarizing petrography (SiC and loose alumina abrasive powders) [4]. To avoid damage to the concrete during preparation, sections were prepared with isopropyl alcohol as a lubricant and excessive heating was avoided. Some concrete pieces were broken in a random way for megascopic examination and SEM observations. Polished samples were carbon coated for EPMA and broken pieces were coated with Au-Pd for SEM observations. Prior to SEM observations, concrete samples were heated in an oven kept at 40 oC for a minimum of 24 h;

(2) EPMA and SEM Polished sections were analysed in a CAMECA

SX-100 microprobe equipped with five WDS

(wavelength-dispersive spectroscopy) detectors (LIF (lithium fluoride), TAP (thallium acid phthalate), PET (pentaerythritol)) and one PGT (princeton gamma tech) prism EDS detector. Operating conditions were set at 15 kV and 20 (observation) or 30 nA (analysis), at high vacuum (< 10-5 Torr). The instrument was calibrated using a range of mineral standards, and resulting detection limits are on the order of 0.02 wt%. Standards were chosen based on their chemical composition to be as close as phases analysed to avoid matrix effect.

Concrete samples were observed under a JEOL JSM-840A scanning electron microscope equipped with an EDXA (energy dispersive x-ray analysis) system. Operating conditions were set at 15 kV. Images were taken in secondary electron mode.

3. Results

3.1 Visual Inspection

The deteriorated concrete displayed map cracking on the walls with open cracks more pronounced at the corners of the foundation walls (Fig. 1). Crack openings often reach up to 10 mm and values as high as 40 mm were reported. Major cracks are often concentrated next to rain gutters, which highlight the role of water or humidity in the reaction and deterioration processes. Yellowish coloration was often seen on the foundation walls. At some locations, iron oxide was visible in the open cracks. Deterioration causes an important breakdown of concrete structures and many foundations had to be replaced (Fig. 2). All the masonry and covering stones were first removed to lighten the structure. Houses were lifted up from their foundations and the later was demolished and replaced. The remediation cost was estimated to be close to the construction cost.

3.2 Petrographic Examination

Several samples of damaged concrete observed under a stereomicroscope and a polarizing microscope showed that the altered concretes were all made with


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the same coarse aggregate containing a certain amount of sulphide minerals. The aggregate used to produce the deleterious concrete foundations was an anorthositic gabbro containing various proportions of sulphide minerals including pyrite, pyrrhotite, pentlandite ((Fe,Ni)9S8) and chalcopyrite (CuFeS2). Other constituting minerals consist mainly of calcic plagioclase feldspars (CaAl2Si2O8), with lesser amounts of biotite (K(Mg,Fe)3AlSi3O10(F,OH)2) and pyroxene (XY(Si,Al)2O6Ca-rich, Na-poor, high-Mg clinopyroxene) (Fig. 3).

The pyrite and pyrrhotite contents vary significantly

from one particle to another and can reach up to 5%-7% of the total coarse aggregate volume (Fig. 4).

The megascopic examination of concrete samples showed alteration on pyrrhotite surfaces. Surfaces were light brown and often covered by rust. Some aggregates were completely disintegrated. The bond between the aggregate particles and the cement paste was often weak. The pyrite surface was unaltered even if some particles were directly in contact with particles of pyrrhotite.

Fig. 5 presents reflected light microscopy images of the aggregate where iron sulphides, pyrite and

Fig. 1 Cracking in house concrete foundation.

Fig. 2 Replacement of the concrete foundation walls.


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Fig. 3 Crushed coarse aggregate (anothositic gabbro).

Fig. 4 Stereomicroscopic view of the anorthositic gabbro aggregate.

Fig. 5 Reflected polarized light views of iron sulphide minerals (Py = pyrite; Po= pyrrhotite).

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pyrrhotite, were in close contact and well disseminated into silicate minerals. Very fine inclusion of opaque minerals can be seen throughout silicates. The observation of polished concrete samples confirms, in several cases, that the pyrite was intact while the pyrrhotite presented evident signs of oxidation.

Fig. 6 presents BSE (back-scattered electron) images of the sulphide minerals taken by EPMA. Pyrite and pyrrhotite are seen in close contact with each other. Pyrrhotite grains appear with a lighter

color than pyrite on the BSE image due to its higher atomic density, with iron content higher and sulphur content lower than for pyrite.

Fig. 7 presents a large grain of pyrrhotite with small inclusions of pentlandite which appear whiter compared to pyrrhotite in BSE image due to their high atomic density. Both minerals showed extended cracking. Black areas in the BSE images correspond to resin or light silicates. Few flame-textured pentlandite exsolved in pyrrhotite can be seen close to grain boundary or along main cracks. Pentlandite is by

Fig. 6 Back-scattered electron images of sulphides minerals within the anorthositic gabbro (Py = pyrite; Po = pyrrhotite).

Fig. 7 Back-scattered electron images of a pyrrhotite grain with pentlandite inclusions gabbro (Po = pyrrhotite; Pe = pentlandite).

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Table 1 Electron probe micro-analysis results measured on pyrrhotite (Po), pyrite (Py) and pentlandite (Pe) grains, results are presented in weight percents.

S Cu Ni Fe Co As TotalPo-1 38.456 0.004 0.588 59.717 0.180 0.000 98.945 Po-2 38.693 0.000 0.503 59.020 0.255 0.011 98.482 Po-3 37.957 0.029 0.681 59.368 0.104 0.000 98.139 Po-4 38.052 0.021 0.674 59.225 0.303 0.000 98.275 Po-5 38.008 0.039 0.688 59.365 0.000 0.051 98.151 Po-6 38.644 0.008 0.363 59.631 0.000 0.015 98.661 MeanPo 38.302 0.017 0.583 59.388 0.140 0.013 98.442 Py-1 52.708 0.002 0.015 47.565 0.000 0.029 100.319 Py-2 52.821 0.000 0.000 47.720 0.000 0.021 100.562 Py-3 52.685 0.000 0.000 47.129 0.000 0.032 99.846 Py-4 52.554 0.023 0.000 47.993 0.000 0.013 100.583 Py-5 52.570 0.000 0.000 47.338 0.029 0.030 99.967 Py-6 52.580 0.000 0.000 47.082 0.134 0.051 99.847 MeanPy 52.653 0.004 0.003 47.471 0.027 0.029 100.187 Pe- 1 32.750 0.000 35.139 28.968 3.548 0.007 100.412 Pe -2 32.646 0.000 35.394 28.700 3.400 0.040 100.180 MeanPe 32.698 0.000 35.267 28.834 3.474 0.024 100.296 Pyrrhotite Fe1-xS where x = 0.099

far more cracked than pyrrhotite. Table 1 presents quantitative microanalysis

determined by EPMA punctual mode on sulphide minerals. According to EPMA analysis, pyrrhotite contains small amount of Ni, Co, Cu and As substituting for Fe in the mineral structure. Analyses are consistent and showed little variations between the different grains analysed. Considering element substitution, x value in the chemical formula of pyrrhotite (Fe1-xS) was calculated to 0.099. Pyrite contains only very small amount of Co and As while content up to 3.47% Co was measured in the pentlandite.

Fig. 8 presents stereomicroscopic views of the deteriorated concrete. In general, the cement paste is highly porous. This is not surprising considering the minimum compressive strength of 15 MPa required for plain concrete used in residential foundation applications. High water-cement ratio in the order of 0.7 is often used for this application. Most of the concrete samples were highly damaged, with important cracking being observed around or through

the aggregate particles and the cement pastes. The bond between the aggregate particles and the cement paste is very weak and some concrete samples can be easily broken in pieces by hand. They were often too damaged to be polished.

Some aggregate particles were extensively cracked, with some cracks extending from the aggregate particles to the surrounding cement paste (Figs. 8a and 8c). Most of the time, cracking occurred next to sulphide rich particles. Sometime, aggregate particles were mostly debonded, as in Figs. 8b and 8c and some particles were completely disintegrated. Fig. 8d is an enlargement showing rust (iron oxyhydroxide/iron sulphate) and a whitish powdery secondary product close to an air void.

Results obtained from stereomicroscopic examinations confirm that the pyrrhotite grains were mainly oxidized while pyrite grains were intact. The nature/composition of the secondary reaction products observed during stereomicroscopic examination was determined by SEM observations.

Fig. 9 shows a pyrrhotite grain on the left end side


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Fig. 8 Stereomicroscopic views of deteriorated concretes.

Fig. 9 SEM images of deteriorated concrete with a pyrrhotite grain (left)in contact with iron oxyhydroxide (right).

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Fig. 10 SEM images of deteriorated concrete with iron sulphate close to pyrrhotite grain.

Fig. 11 SEM images + EDXA analysis of gypsum present in deteriorated concrete.

of the micrograph, in close contact with an iron oxide, hydroxide or oxyhydroxide. The precise nature of the oxidation product can not be determined using EDXA because hydrogen is not detected. The EDXA signal (not presented) shows the x-ray lines of iron (Fe) and oxygen (O). Fig. 10 shows a layer of an iron sulphate next to a pyrrhotite grain. The EDXA signal shows the x-ray lines of iron (Fe), sulphur (S) and oxygen (O) (not presented). These secondary products are associated to the reaction of pyrrhotite. Fig. 11 exhibits a grain of gypsum (calcium sulphate dehydrate) with corresponding EDAX spectrum. SEM

observations have confirmed the identification of secondary minerals/phases, mostly iron oxide, hydroxide or oxyhydroxide, iron sulphate and gypsum near altered pyrrhotite grains.

4. Discussion

Based on petrographic examination, pyrrhotite was determined as the deleterious mineral phase in the concrete samples. It is well-known in the mining environment literature that sulphide minerals are unstable in oxidizing conditions. Upon exposure to water and oxygen, sulphide minerals oxidize to form

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acidic, iron and sulphate-rich by-products according to the following equations [5]:

Fe1-xS + (2 - x/2) O2 + xH2O (1-x) Fe2+ + SO4 2- + 2x H+ (1)

The oxidation of ferrous iron (Fe2+) produces ferric ions (Fe3+) that can precipitate out of solution to form ferric hydroxide, if pH is not too low. Fe2 + is oxidized and precipitated as ferric oxyhydroxides, principally ferrihydrite and goethite.

Fe2+ + 1/4 O2 + 2H+ Fe3+ + H2O (2) Fe 3+ + 3H2O Fe(OH)3(s) + 3H+ (3)

The oxidation reaction of iron sulphides occurs only in the presence of oxygen and of humidity and generates various mineralogical phases [5-7]. According to Grattan-Bellew and Eden [8] and Shayan [9], the sulphuric acid generated through this process reacts with the solids of the cement paste, and particularly with the portlandite (Ca(OH)2), to form gypsum according to the following equation:

H2SO4 + Ca(OH)2 CaSO4 2H2O (gypsum) (4) The attack of concrete by sulphates resulting from

the oxidation of sulphide-bearing aggregates would produce the crystallization of secondary ettringite following the reaction with the alumina-bearing phases of the hydrated portland cement paste (Eq. (5)). According to Divet et al. [10], high pH conditions, as those found in concrete, enhance iron sulphide oxidation.

3(CaSO4 2H2O) + C3A+ 26 H2O C3A 3CaSO4 H32 (ettringite) (5)

In a general way, secondary products most frequently generated during the oxidation of iron sulphides are the rust under all its forms (goethite (FeOOH), limonite (FeO (OH) nH2O)), sulphates including gypsum and ettringite. Degradation of concrete is thus due to the combined mechanisms of oxidation of iron sulphides followed by sulphatation in the cement paste. Both reactions create secondary minerals that cause expansion. According to Casanova et al. 1996 [11], the later is by far more expansive. In fact, during the formation of gypsum, the volume of

the resulting products represents a little more of double of that of the starting solids.

According to the scientific literature, the cases of deterioration of the concrete due to the oxidation of sulphide minerals were reported for porous and mechanically weak rocks such as black shale [11-14]. In the present case, the aggregate is an anorthosic gabbro with low porosity and despite its good mechanical performances, major damages were noticed only two to four years after construction. As mentioned before, the presence of oxygen and water is necessary for the oxidation reaction. Conditions were favourable for sulphide oxidation and it is possible that presence of other sulphide minerals (pyrite, pentlandite, chalcopyrite) can have played a role of catalyst increasing the kinetic of pyrrhotite reaction. The role or synergy of other sulphide minerals should be investigated.

5. Conclusions

Cases of degradation of concrete associated to iron sulphides-bearing aggregates were recently recognized in the Trois-Rivires area, Canada. This study reports result of site inspection along with concrete cores characterisation using different petrographic tools including stereomicroscope, polarizing microscope, SEM and EPMA. Main results show that:

Deteriorated concrete display map cracking, yellowish coloration, open cracks more pronounced at the corners of the foundation often next to drainage elements;

The problematic aggregate is an anorthositic gabbro containing iron sulphide minerals;

Iron sulphides are finely disseminated into silicate minerals;

Pyrrhotite is oxidized while pyrite is not, the former contains Ni, Co, Cu and As substituting for Fe;

Considering element substitution, x value in the non-stoichiometric mineral chemical formula (Fe1-xS) was calculated to 0.099 in the pyrrhotite studied;


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Concrete samples are highly damaged, with important cracking observed around and through the aggregate particles and the cement paste, and some particles completely disintegrated or debonded;

Secondary minerals identified are iron oxide/hydroxide/oxyhydroxyde, iron sulphate and gypsum;

The oxidation of pyrrhotite followed by sulphatation of the cement paste seems to be the main mechanism of concrete deterioration.

Further research is needed to develop a quality control test to identify potentially deleterious aggregates.

Acknowledgments

This study has been supported by the National Science and Engineering Research Council of Canada (NSERC) and by the Fonds de recherche sur la nature et les technologies of the Province of Qubec (FQRNT).

References

[1] J.P.R. de Villiers, D.C. Liles, The crystal-structure and vacancy distribution in 6C pyrrhotite, American Mineralogist 95 (2010) 148-152.

[2] D.C. Liles, J.P.R. de Villiers, Redetermination of the structure of 5C pyrrhotite at low temperature and at room temperature, American Mineralogist 97 (2012) 257-261.

[3] M. Becker, J. de Villiers, D. Bradshaw, The mineralogy and crystallography of pyrrhotite from selected nickel and PGE ore deposits, Economic Geology 105 (2010) 1025-1037.

[4] D. Jana, Sample preparation techniques in petrographic

examinations of construction materials: A state-of-the-art review, in: ICMA Conference Proceedings of the 28th Conference on Cement Microscopy, Denver, USA, 2006, pp. 23-70.

[5] N. Belzile, Y.W. Chen, M.F. Cai, Y. Li, A review on pyrrhotite oxidation, Journal of Geochemical Exploration 84 (2004) 65-76.

[6] Y.L. Mikhlin, A.V. Kuklinskiy, N.I. Pavlenko, V.A. Varnek, I.P. Asanov, A.V. Okotrub, et al., Spectroscopy and XRD studies of the air degradation of acid-reacted pyrrhotites, Geochimica and Cosmochimica Acta 66 (2002) 4057-4067.

[7] H.F. Steger, Oxidation of sulphide minerals: VII, Effect of temperature and relative humidity on the oxidation of pyrrhotite, Chemical Geology 35 (1982) 281-295.

[8] P.E. Grattan-Bellew, W.J. Eden, Concrete deterioration and floor heave due to biogeochemical weathering of underlying shale, Canadian Geotechnical Journal 12 (1975) 372-378.

[9] A. Shayan, Deterioration of a concrete surface due to the oxidation of pyrite contained in pyritic aggregates, Cement and Concrete Research 18 (1988) 723-730.

[10] L. Divet, J.P. Davy, Study of pyrite oxidation risk in the basic medium of concrete, LCPC Bulletin 204 (1996) 97-107. (in French)

[11] I. Casanova, L. Agullo, A. Aguado, Aggregate expansivity due to sulphide oxidationI. Reaction system and rate model, Cement and Concrete Research 26 (1996) 993-998.

[12] J. Berard, R. Roux, M. Durand, Performance of concrete containing a variety of black shale, Canadian Journal of Civil Engineering 2 (1975) 58-65.

[13] J.S. Chinchon, C. Ayora, A. Aguado, F. Guirado, Influence of weathering of iron sulfides contained in aggregates on concrete durability, Cement and Concrete Research 25 (1995) 1264-1272.

[14] C. Ayora, S. Chinchon, A. Aguado, F. Guirada, Weathering of iron sulfides and concrete alteration, Cement and Concrete Research 28 (4) (1998) 1223-1235.


Behavior of Millstone Masonry Vaults Strengthened by

Composite Materials

Maamoun Saade1, 2, Stephan Kesteloot1, Chafika Djelal1, Lotfi Hamitouche2 and Idriss Benslimane2 1. Laboratoire Gnie Civil et Go-Environnement (LGCgE)Lille Nord de France, IUT de Bthune, Bthune 62400, France

2. Structure & Rhabilitation, Bagnolet 93170, France Abstract: Sewerage systems first appeared in Paris in the middle of 19th century. Even if the majority of structures are still in working order, their general state will deteriorate inexorably, and as reconstruction is not always possible for cost and social impact reasons, rehabilitation is a solution adopted by many clients. It is necessary to resort to new rehabilitation techniques. Reinforcement by bonding composite materials has many advantages compared to other techniques. The objective of the experimental campaign presented in this paper is to study the addition of a lining by means of mortar reinforced by thin composite materials so as to restore masonry structures. To that purpose, crushing tests on masonry vaults have been carried out. The application of a lining made of mortar reinforced with composite materials has allowed increasing the breaking load and delaying the occurrence of the first cracks. This article presents the characterization of the materials. Moreover, the results of the breaking tests applied to masonry vaults are shown in this paper. A comparison with a traditional type of rehabilitation by a 6 cm-thick shotcrete lining will be performed. Key words: Composite materials, masonry, fiber coating, sustainability, rehabilitation, sewerage systems.

1. Introduction

French man accessible main sewers have a total length of several dozen thousand kilometers. Yet, some of these sewerage systems have often exceeded their useful life. The different forms of degradation present on these structures (ageing, environment) require a total or punctual rehabilitation. Most masonry sewerage systems managers have to face the problem of budgetary restrictions and have to raise substantial volumes of finance so as to rehabilitate their structures while seeking the best suited economic and technical solutions. Main sewers, mainly made of millstone masonry in big French cities show signs of damage, the most often listed of which are surface deterioration, structural degradations, leaks and cracking [1]. The authors study mainly deals with egg-shaped, man accessible wastewater facilities made of millstone and known as main sewers. These structures consist of a vault, abutments and a raft (Fig. 1).

Corresponding author: Maamoun Saade, Dr., Ph.D. student, research field: reinforcement by composites materials. E-mail: [email protected].

The most widely used technique to rehabilitate the majority of sewerage systems is to apply a 6 to 8 cm-thick reinforced shotcrete lining to the entire section of the main sewer. The greatest disadvantages of this technique lie in a significant reduction of the hydraulic section, costs exceeding the budget, problems of corroding reinforcement and buckling steel. For these reasons, it is interesting to implement a new reinforcement technique. The repair and

Fig. 1 Ovoid sewer.

Vault

Masonry

CoatingAbutmentwall

Invert

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Behavior of Millstone Masonry Vaults Strengthened by Composite Materials

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strengthening of the structures by bonding composite materials have shown good results in the field of construction and has recently been applied to concrete sewerage systems [2].

The main goal of this research is to adapt this rehabilitation process to masonry sewerage systems. Besides, response times on site are cut down in order to rehabilitate a greater length of network without using corrodible materials. The project initiated by a consulting firm and several French companies aims to reduce costs, improve repair durability (without the use of steel reinforcement) and reduce response times on site.

2. Composite Materials in Structures

Over the past 30 years, researchers have studied the possibility of using innovative materials like composite materials to strengthen masonry structures. Two types are commonly used in the construction industry, extruded carbon plates and carbon fabrics. Composite materials have considerable advantages such as lightness, insensitivity to corrosion, ease of application.

Many tests were carried out in Italy on masonry vaults as part of the protection of the cultural heritage against seismic hazards (CNR-DT, 2004).

(1) Aiello et al. [3] developed experimental studies for the strengthening of masonry arches, indicating that the application of CFRPs increases the strength of the structure, and modifies the failure mechanism and breaking load;

(2) Valluzzi et al. [4] presented the results of tests performed on masonry arches made of brick and reinforced with fabrics made from carbon or glass fiber on the intrados or on the extrados. The breaking loads are the same for both types of reinforcement but the failure mechanism is different;

(3) Luciano et al. [5] showed the effectiveness of masonry arches strengthened with carbon plates and their numerical calculations reproduced the same behavior for the tested arches.

However, bonding techniques for composite materials are not directly applicable to masonry sewerage systems due to the irregularity of the substrate. It is necessary to apply a thin lining having the appropriate characteristics to transmit the load of the masonry onto the composite materials.

Tests on masonry vaults reinforced with a 3 cm-thick fiber coating have been conducted by Ref. [6], in order to show the relevance of the putting in place of a thin lining to rehabilitate main sewers.

Indeed in some cases, it is not necessary to reinforce the structure but to simply get a facelift for example during infiltration or exfiltration. A thin lining is designed to homogenize the vault surfaces. The study showed a significant increase in the load by about 208% and a lower repair cost compared to the method of the 6 cm-thick shotcrete.

Characterization tests of the materials used are presented as well as tests on millstone masonry vaults, coated and reinforced by composite materials (carbon plates or fabrics) at the intrados. A comparison with a traditional rehabilitation method by means of reinforced shotcrete will be drawn.

3. Test Specimen Selection

Because of complexity of the material and the geometry of the structure, it is necessary to adopt a simplified geometry in order to perform laboratory tests. Furthermore, a masonry ovoid sewer is not stable under its own weight, hence the need to use lateral stops. In most cases, reinforcement is necessary with vertical loads that mainly put a strain on the vault. The test specimen chosen for this study are vaults built according to the numerical calculations made by Ref. [7]. They must correspond to the upper part of the ovoid, between the springs of the vault, close to the two hinges, at abutment/vault level. The test specimens are vaults representing the vault of a T210 ovoid sewer whose geometric characteristics are given in Fig. 2. The vault has a width of 110 cm and a length of 120 cm.

Behavior of Millstone Masonry Vaults Strengthened by Composite Materials

934

Fig. 2 Geometric characteristics of T210 ovoid section and test piece.

After these generalities, the mechanical properties of the different materials (millstone, bonding mortar, fiber coating and composite materials) are given in the following paragraph. The results concerning the full scale vaults are then discussed.

4. Experimental Tests

The mechanical properties of the millstone, the bonding mortar, the fiber coating, the carbon plates and sheets and their associated adhesives are as follows:

(1) Millstone: The blocks used to build vaults; (2) Bonding mortar: The bonding mortar between

the different blocks has been made according to bibliographic research [8].

Table 1 presents the mechanical characteristics of the millstone and the mortar.

All the results obtained during the characterization tests show that millstone is a material with widely disparate mechanical properties (different colors, more or less important cavities, etc.). This mortar has been chosen for the authors experimental campaign in view of its mechanical properties, similar to those used in the construction of sewerage systems in the nineteenth century. The bonding mortar is similar to the authors according to the three above given criteria (modulus of elasticity, compressive strength and flexural strength);

(3) Fiber coating: The coating should allow transferring loads to the composite reinforcements. The fiber coating selected for this study is one whose mechanical characteristics are best suited for the transmission of loads to composites. The fiber coating

is a fiber-reinforced mortar used for repairs. It is used for resurfacing and restoration works. Table 2 presents the mechanical characteristics of the fiber coating;

(4) Composite materials: For the study, the authors strengthened the vaults by means of carbon plates and sheets. These processes are intended to repair and strengthen structures. The plates are composite materials made of carbon fibers embedded in a polymer matrix and the sheets are a carbon fiber matrix. Their mechanical properties are summarized in Table 3.

To apply the composite reinforcements to the fiber coating, the authors used a type of glue for each type of epoxy-based reinforcement. The role of the adhesive is very important in the case of reinforcement by composite materials, due to the transmission of forces into the structure of the composite materials. The mechanical properties of the different types of glue are summarized respectively in Tables 4 and 5. Table 1 Mechanical characteristics of millstone and bonding mortar. Designation Millstone Mortar Modulus of elasticity (MPa) 2,500 5,931 Compressive strength (MPa) 12 to 26 0.9 Tensile stress (MPa) 1.47 - Flexural strength (MPa) - 0.5

Table 2 Mechanical characteristics of fiber coating.

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