the mechanical performance of folded ferrocement …

Journal of Engineering Science and Technology Vol. 15, No. 6 (2020) 4200 - 4213 © School of Engineering, Taylor’s University

4200

THE MECHANICAL PERFORMANCE OF FOLDED FERROCEMENT ELEMENT AT DIFFERENT AGING PERIODS AND HOT CLIMATES

MUYASSER M. JOMAA’H1, SAAD R. AHMED2,*, MAZIN B. ABDULRAHMAN1, FIRYAL ADHOE1, ZARAA SAMI1

1Civil Department, College of Engineering, Tikrit University, Iraq. 2Mechanical Department, College of Engineering, Tikrit University, Iraq

*Corresponding Author: [email protected]

Abstract

Roofing elements is one of the most widely used applications of folded ferrocement for both industrial and domestic buildings. Owing to this wide application, more advanced mechanical properties are required for these elements. Among these mechanical properties, mechanical capacity against fracture and harsh climate are two essential properties must be acquired. Thus, the present investigation was conducted to fabricate a high strength and environmental resist folded ferrocement elements. Cubes of the specimens were prepared by folding technique at 50×50×50 mm size with specific enforcement. These samples were exposed to a hot environment at different time intervals then examined for compressive strength. Also, the modulus of rupture was determined at different temperatures-time strategies for the standard prisms prepared with the dimensions of 40 × 40 × 160 mm. It was found that the preparation method of folding gave a high quality folded ferrocement in terms of flexural and climate resistance. It was also found that the fabricated sheets were cost-effective compared to the conventional ferrocement sheet at the same testing environments and the choice of folded sheets contributes to reduced load intensity and reduced deflection.

Keywords: Folded ferrocement, Flexural test, Roofing elements, Temperature.

The Mechanical Performance of Folded Ferrocement Element at Different . . . . 4201

Journal of Engineering Science and Technology December 2020, Vol. 15(6)

1. Introduction In developing countries where the climate is obviously hot, the most essential components in housing construction are roofing, floors, and walls. To obtain a comfortable environment it is required to intensively work on developing lightweight construction materials that exhibit particular characteristics such as high mechanical strength, and durability [1, 2]. Ferrocement has proven itself as an excellent for roofing of buildings as it is successfully presented in ferrocement composites. These composites were utilized for their outstanding properties of mechanical strength, light weighs, water resistance, and brightness [3]. Ferrocement is also used for other applications such as water tank, grain silos, canal lining, and some special applications as a precast sandwich wall, ferrocement water filters, ferrocement segmental shells, etc. [4] Ferrocement offers the possibility of producing relatively light prefabricated structural elements, up to 70% of the traditionally reinforced concrete elements, which can be formed into interesting architectural elements for low-cost housing. As a versatile material, ferrocement has been used for the production of prefabricated components required in building construction [5]. Research investigations into the application of ferrocement composite for the improvement of mechanical and isolation properties of building elements have reported great potential [6-8].

For this purpose, it is also needed to acquire the environment to resist property as a crucial property needed to prolong the lifetime of the roofing sheets. Owing to these required properties and due to slenderness of these sheets, numerous workers were interested to investigate the effect of adding different components such as paints, nanomaterials, fibers or metals to the cement matrix to obtain a successful roofing/flooring ferrocement sheet. These applications motivated the innovators to develop different methods of making desirable and marketable ferrocement sheets. Romeo and Zinzi [9] showed that the use of cool paint reduced the peak temperatures of the roof surface and indoor air by 20°C and 2.3°C respectively.

Alvarado et al. [10] studied the thermal effects of their designed passive cooling systems on concrete roofs in existing buildings. Double envelope roof constructions were investigated either as a preheating system of the external air [11] or as a double shell system in tiled roofs. Although the benefits of using cool roofs or coatings were revealed in many experimental studies, one major disadvantage of cool material is that its solar reflectance tends to degrade over time due to the aging and weathering [12, 13].

Folded ferrocement element have been used widely as an efficient material for reducing extreme temperature. Folded sheet roofing elements are fabricated by two basic methods, the conventional molding and folding [14]. Over the molding technique, the folding technique showed several advantages and it is preferable in the roofing of buildings. Among these advantages are cost-effective, lightweight and smoothness of the sheets. Considering the economy of construction, the folding technique provides an attractive alternative in the construction of folded plate roofing elements. It was found that the outstanding performance of the folded ferrocement sheets attributed to the impact of ferrocement [15]. In addition to ferrocement, the addition of fibers as a reinforcement attracted several researchers.

Clarke [16] presented the results of structural testing of the full-scale ferrocement roof system. The dimensions were 9.0 m wide and 2.5 m high pitched-portal frame of channel-section with bolted steel connections; a 6.10 m hollow-section roof slab in bending, and slab-to-frame bolted connections in a pull-out. It was found that the performance of the elements is consistent with the acknowledged beneficial

4202 M. M. Jomaa’h et al.


behaviour of ferrocement and meet the loading conditions expected in the region of study. Also, contributions such as the work of Basunbul et al. [17] described the behaviour of ferrocement element under the impact of earthquake. The behaviour of structure was found satisfactory and cost effective due to the use of glass fibers as a reinforcement unit.

Alavez-Ramirez et al. [18] used coconut fibres as a reinforcement for a ferrocement roofing element. They found that these fibers gave an energy saving and thermally comfort roofing units. Thanoon et al. [19] introduced a designed and semi-fabricated a slab panel consists of two layers for flooring. The first one is made of a precast ferrocement and the second one consists of bricks and mortar. They investigated the response of this flooring material for flexural impact and found that the performance of the composited fabricated was satisfactory and it can be used as a flooring material.

Majeed and Mahmod. [20] describes the results of testing folded and flat ferrocement panels reinforced with a different number of wire mesh layers. They found that the panels tested showed good performance under flexural loads. Rajaiah et al. [21] investigated the flexural behaviour of the folded ferrocement panel reinforced with a number of wire mesh layers. They used different numbers of wire mesh layers and examined their effects on cracking, load-deflection behaviour, ductility and ultimate flexural strength. They found that increasing the number of wire mesh layers has a positive impact on the ductility and capability to absorb the energy of the tested panels.

Kesava et al. [22] investigated the mechanical properties of a ferrocement folded plate used for roofing industrial sheds. They developed a procedure of ferrocement roofing on reinforced concrete frame with six bays of (14 m × 4.57 m). the folded plates roofing elements were precast in an effective size, hoisted and joined in a suitable position. It was proved that the developed units are satisfies the mechanical and environmental requirements of industrial sheds.

This is useful to find solutions by searching for new design techniques and methods of construction. Thus, numerous researchers developed different methods and composites to improve the performance of roofing elements against loading and weathering conditions. The present study aims to design a folded ferrocement roofing element capable of withstanding high mechanical loads and extremely hot weather. Also, this investigation studies the effect of aging on these capabilities.

2. Experimental Work

2.1. Fabrication of ferrocement roofing panels Sieve analysis of fine aggregate was conducted according to the ASTM C136/C136M [23]. Iraqi cement which is made according to the specifications of ordinary Portland cement (type I) was used in the present study. Tables 1 and 2 show the physical and chemical properties of the cement respectively. For reinforcement, steel wire meshes are utilized as primary reinforcement. A galvanized chicken wire mesh with a 12 mm square opening and 0.68 mm wire diameter was used in the present investigation. Table 3 shows the mechanical properties of the galvanized wire mesh screens.



Table 1. Physical properties of cement [24]. Limit of Iraqi

specification No. 5\1984 Experimental measurement Physical Properties

(230 m2/kg) lower limit 346 m²/kg Specific surface area

(Blaine method)، (m2/kg)

Not less than 45min Not more than 10 hrs.

3 hrs. 5 min 5 hrs. 20 min

Setting time (vacate apparatus) Initial setting، (hrs.: min) Final setting، (hrs.: min)

Not less than 15 MPa Not less than 23 MPa

22.7 MPa 27.7 MPa

Compressive strength (MPa) For 3-day For 7-day

Table 2. Chemical properties of cement [24].

Limit of Iraqi Specification No.5\1984 Content % Oxides Composition

- 62.03 CaO - 4.91 Al2O3 - 20.83 SiO2 - 2.98 Fe2O3

5 % Max 2.21 MgO 2.5 % Max 2.2 SO3

4 % Max 1.24 Loss on Ignition، (L.O.I)

1.5 % Max 0.42 Insoluble material

(0.66-1.02) 0.91 Lime Saturation Factor (L.S.F)

Main Compounds

Limit of Iraqi Specification No.5\1984 Content % Oxides Composition

- 50.64 C3S - 21.7 C2S

< 5 % 4.2 C3A - 9.071 C4AF

Table 3. Mechanical properties of the wire mesh (enforcing material).

Type of Reinforcement

Diameter (mm)

Yield Stress (Fy), (MPa)

Ultimate Strength (Fu),

(MPa)

Modulus of elasticity (E),

(MPa) Wire Mesh 0.68 389.4 412.8 61981

The size of cubes prepared in this study, according to ASTM C109 / C109M [25], is 50 x 50 x 50 mm and 40 x 40 x 160 mm.. The cubes were reinforced by steel mesh wires, three samples of each specimen were cast with different wire/cement ratio to obtain good strength and high workability then they were cured over 28 days. The modulus of rupture for the samples of cement mortar prism was calculated via equation 1 [26];

𝑓𝑓𝑟𝑟 =3𝑃𝑃𝑃𝑃𝑏𝑏𝑑𝑑2

(1)



where; fr: modulus of rupture (MPa), P: line load (kN), d: height of prism (mm), and L: Length of the prism (mm), b: width of the prism (mm).

Figure 1 shows the sample under the rupture test in (UTEST Flexural Machine, Turkey). For heating the samples, three sets of thermocouples type K were installed, one at the center of the cube and the other two at the edge. The thermocouples were joined to an electrical heater to supply the heat required.

Fig. 1. The prism during the test.

Then, the galvanized steel mold with a 300 mm length of the specimen was fabricated (Fig. 2(a)). The mortar was placed vertically inside the mold prior to conditioning. A sample of the molded specimen is shown in Fig. 2(b).

(a)

(b)

Fig. 2. (a) Dimensions of the steel mold used in the present study; (b) The mold of the composite.



2.2. Testing of flexural behaviour The folded sample was placed inside the apparatus of flexural behaviour and the dial gauge was placed at the center of the sample to record readings of deflection; then the rate of the load was increased at 5 kg/s [27] to develop a load-deflection curve. Then The cracks generated in the sample were tracked and coloured (Fig. 3).

Fig. 3. (a) Sample before testing; (b) Sample during testing; and (c) Sample after failure and determine the cracks lines.

3. Results and Discussion In the present work different tests have been conducted according to the experimental plan. The observations on the measurements were discussed as given in the sections below.

3.1. Effect of curing time and time of exposure on compressive strength The results of the compressive strength of the specimens of ferrocement roofing sheets reinforced with a wire mesh are presented in Table 4. It shows the response of the specimens at 1:2 mix ratio and different environments, with and without heating, at different times of exposure and ages of curing. The reduction in compressive strength is depicted obviously in Table 4 that is the average compressive strength was reduced by 37.9%, 55.4% and 61.1% for 60 min, 120 min and 180 min time of exposure respectively for the specimens cured for 7 days. As the age of curing was increased to 28 days, compressive strength exhibited a noticeable improvement in response to heating that is less reduction was observed, 26.4%, 46.4% and 54.8% for 60 min, 120 min and 180 min respectively. The impact of longer aging time on improvement of compressive strength is clearly seen in Fig. 4, a similar behaviour was reported by Majeed and Mahmod [20] and the reported result of the compressive strength obtained is the present study without heating at 1:2 ratio (48.9 MPa) is higher than the value reported by Rajaiah et al. [21] for the same ratio (47.25 MPa).

(c)

(b) (a)



From Table 4 and Fig. 4 can be seen that the designed folded ferrocement showed a satisfactory performance at different times of exposure to heat. As the time of exposure going longer, the change in compression strength becomes less progressively. Because compressive strength is very sensitive to density, the sheets (composite) mixes may have more voids than mortar mixes. As the time of aging differs, the voids may merge or be filled with the matrix of the composite or the wire mesh causing that obvious change in compressive strength. In case, these voids were not filled or merged uniformly, the compressive strength experienced a fluctuation of results. However, the change in the compressive strength reported in this study are noticed to be affected by extensive exposure to heat (i.e., as the time of exposure was prolonged) because the water content in the composite was vaporized and resulted in reducing the composite density.

Table 4. Compressive strength of 1:2 mix specimens at different environments and age of curing.

Time Without heating 60 min 120 min 180 min

Age Cube sample no. and compressive strength (MPa)

Cube sample no. and compressive strength (MPa)



1 2 3 1 2 3 1 2 3 1 2 3

7 days 35.92 34.53 38.15 22.05 25.32 20.04 19.03 15.67 15.322 15.61 12.25 14.56 Av= 36.202 Av= 22.466 Av= 16.67 Av= 14.143

28 days

44.39 52.95 49.61 39.42 35.04 34.05 25.34 28.56 24.62 23.05 20.87 22.33 Av= 48.9 Av= 36.16 Av= 26.17 Av= 22.071

Fig. 4. The effect of time of exposure on compressive strength of cement mortar at 1:2 mix rate at different age of curing.

For the 1:1 mix ratio, Table 5 and Fig. 5 shows the experimental results of the compressive strength tested against aging and time of exposure to heat. The obtained result (64.1 MPa) also showed a higher improvement compared to Rajaiah et al. [21] (52.16 MPa). The improvement in compressive strength attributes to the increase of the folded ferrocement [22]. Compared to the results obtained at ambient temperature (without heating) the average compressive strength was reduced by 38.5%, 48.23% and 51.1% for 60 min, 120 min and 180 min exposure to heat respectively for the specimens cured for 7 days. As the age of curing was increased to 28 days, compressive strength



showed a noticeable improvement in response to heating that is the above percentage of reduction was enhanced to 22.4%, 37.6% and 33.8% for 60 min, 120 min and 180 min respectively. Again, giving more time for aging of specimens would provide the time needed for the cement mixture to build the network with the ferrous and wire mesh which is required to obtain a strong composite and explains the noticeable improvement for the latter results.

Table 5. Compressive strength of (1:1) mix ratio at different time of exposure to heat. Time Without heating 60 min 120 min 180 min

Age Sample no. and

compressive strength (MPa)

Sample no. and compressive

strength (MPa)


strength (MPa)


strength (MPa) 1 2 3 1 2 3 1 2 3 1 2 3

7 days 41 50 48.8 32.1 34.6 30.2 26.4 27.8 27.4 25.7 27.8 23.7 Av= 52.6 Av= 32.34 Av= 27.25 Av= 25.79

28 days 60.3 67.7 65.3 49.9 50.4 48.7 41.05 40.6 44.2 46.8 42.1 38.2 Av= 64.1 Av= 49.7 Av= 41.9 Av= 42.405

Fig. 5. The effect of time of exposure on compressive strength of cement mortar at 1:1 mix rate at different age of curing.

3.2. Effect of curing time and time of exposure on the modulus of rupture (fr) It is helpful to utilize modulus of mechanical properties to estimate the intrinsic change in particular mechanical properties due to exposure to different environments. Modulus of rupture is one of these moduli. It is widely applied in investigations of ferrocement structures. Table 6 and Fig. 6 show the results of the modulus of rupture of the specimens of the prisms fabricated in the present study tested at different times of exposure with and without heating for 1:1 mix ratio. It can be noticed that the modulus of rupture is drastically reduced from 5.26 MPa for prism tested at room temperature to 4.47 MPa for the prisms exposed to heat for 60 min. Moreover, the modulus is almost diminished and falls to a stationary value (0.35 MPa) as the time of exposure to heat increases to 120 min and longer. These results agreed with the findings of Corinaldesi and Moriconi [28] and Drzymala et al. [29].

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Table 6. Modulus of rupture for 1:1 mix ratio with different time of exposure to heating. Time Without heating 60 min 120 min 180 min

Age Prism no. and

refractive index (MPa)

Prism no. and refractive index

(MPa)


(MPa)

Prism no. and refractive

index (MPa) 1 2 3 1 2 3 1 2 3 1 2 3

7 days 4.7 4 3.5 3 3.25 3.5 2.5 2.1 2 0.4 0.5 1 Av= 4.06 Av= 3.25 Av= 2.2 Av= 0.63

28 days 10.3 11.6 11.5 9.37 9.1 9 4.64 4.626 4.55 0.36 1.63 1 Av= 11.17 Av= 9.16 Av= 4.6 Av= 0.99

Fig. 6. Modulus of the rupture-age relationship of cement mortar of 1:1 mix rate at different times of exposure.

Table 7 and Fig. 7 depicts the impact of using a 1:2 mix ratio in the fabrication of the folded ferrocement composite on the modulus of rupture. As shown in Table 7, the rate of development of strength was high at an early age but greatly reduced at later ages. This increase in strength at early ages and decrease at later ages may be attributed to the rough cement aggregates formed upon solidifying of the mortar. According to Mehta and Monteiro [30], a stronger physical bond between the rough-textured aggregate and the cement paste is responsible for the increased tensile strength at an early age. At later ages, however, when chemical interaction between the aggregates and the paste begins to take effect, the effects of the surface texture may not be as important [31]. The results shown in Table 7 shows that modulus of rupture obtained in the present study is much higher the relevant values obtained by Majeed and Mahmood [20] and Rajaiah et al. [21].

Table 7. Modulus of rupture for 1:2 mix ratio with different time of exposure to heating.

Time Without heating 60 min 120 min 180 min

Age Prism no. and

refractive index (MPa)


(MPa)

Prism no. and refractive

index (MPa)


(MPa) 1 2 3 1 2 3 1 2 3 1 2 3

7 days 5.1 6 4.67 4 5.03 4.37 3.2 2.9 3.5 0.05 failure 1 Av= 5.26 Av= 4.47 Av= 0.35 Av= 0.35

28 days 12.9 13.3 13.1 10.6 9.2 9.5 6.4 5.12 4 failure 0.28 1.14 Av= 13.13 Av= 9.78 Av= 5.18 Av= 0.47



Fig. 7. Modulus of the rupture-age relationship of cement mortar of 1:2 mix rate at different times of exposure.

3.3. Effect of curing time and time of exposure to load-deflection relation The measurements of load against mid-span deflection were presented in Table 8 and Fig. 8 for the fabricated prisms with all examined mixes. Initially, as the load increases, the deflection also increases linearly up to a certain load, yield load and after that point, the mid-span deflection varies nonlinearly and reaches the maximum value. Beyond the ultimate load point, the deflection starts increasing appreciably with the decrease in load. However, the impact of aging time is obvious in Fig. 8 as reducing the exposure time to heating revealed less deflection for the two mixes ratio despite that the ratio of 1:1 showed better performance and it is evident that the ultimate load-carrying capacity of associated with 0.7 mm deflection at 60 min time of exposure. For the longer times, the deflection reached 1 mm and higher at the two ratios of mixes. The load-deflection results show that the fabricated composite with a mix ratio of 1:1 exhibits satisfactory behaviour as it exposed to heating. It also shows that as the time of exposure to heating increases from 60 to 120 min the deflection decreases from 0.7 to 0.55 mm (21.4% of reduction). However, as the mix ratio shifts to 1:2, the percent of reduction decrease to 12.5%.

Table 8. Load-deflection measurements for the two mixes ratio at different times of exposure.

Sample no.

Deflection (mm)

Load (kN)

Rate Mix

Exposure time to heat (min)

1. 0.55 7.6 1:1 120 2. 0.9 8.65 1:2 120 3. 0.7 7.85 1:1 60 4. 0.75 7.5 1:1 180 5. 0.8 8.85 1:2 60 6. 0.85 6.689 1:2 180 7. 0.9 13.5 1:2 Without heating 8. 1.5 10.618 1:1 Without heating



(a) without heating.

(b) with heating at 200oC for 60 min.

(c) with heating at 200oC for 120 min.

(d) with heating at 200oC for 180 min.

Fig. 8. The flexural capacity of a folded element of (1:1) and (1:2) mix.



3.4. Mode of failure The decrease in compressive strength for cubes at different mix ratio is due to increasing the time of exposure to heating. The same reason was behind the decrease of the modulus of rupture for the prisms tested. Regarding the folded ferrocement samples they are also affected by the long duration of exposure to heat that is owing to the decrease in stiffness and ultimate load. Compared to the deflection of the reference sample (without heating) it was also observed that the deflection increases as the exposure time to heating increases. The folded ferrocement sample with a 1:2 mix ratio has shown higher resistance to failure and its deflection has been lower compared to deflection measured for 1:1 mix ratio which indicates higher ductility for the 1:2 mix samples. Thus, these properties allow the sample to bend because of the presence of the layers of steel wire mesh. That was seen at the time of testing as all cracks observed for these samples were linear (as shown in Fig. 3(c)), i.e., the failure is elastic, and the load-deflection relationship is semi-linear. Also, the load was transferred to the webs in the sample. Figure 9 shows all samples tested after failure.

Fig. 9. The samples after failure.

4. Conclusions The response of a locally fabricated folded ferrocement prisms was examined at different times of exposure and aging times for the purpose of assessing the performance as a possible roofing element. It was crucial to study the mechanical behaviour of these composites as building roofs are frequently exposed to extremely different climates and loads. The most significant findings are concluded as follow:

• The cracks observed in ferrocement folded sheets late are started at load point zone despite there was enforcement dispersed and the crack width is comparatively less than the conventional sheets.

• The deflection was reduced obviously by enforcement although the exposure time to heating was longer compared to the deflection of the reference sample that was deflected without heating.

• The folded ferrocement sample for mix ratio 1:2 has shown higher resistance to failure at a longer time of exposure and its deflection value has been lower compared to mix ratio 1:1. In contrast, the 1:1 ratio possesses more ductility at the least exposure time of 60 min to heating. Thus, the sheets were able to bend with the reinforcing steel which has high flexibility.



• The behaviour of the ferrocement sample can be described by the cracking stage in this stage all materials are elastic the load-deflection relationship is semi-linear. the load is transferred to the webs in the sample.

• It is generally concluded that the use of ferrocement in folded sheets given good results since folded plates are useful for longer span the ferrocement made the members thinner for carrying loads and resist harsh climates.

Nomenclatures b Width of the prism d Height of prism 𝑓𝑓𝑟𝑟 Modulus of rupture L Length of the prism P line load

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