EVALUATION OF PROPERTIES OF WORKABLE POROUS CONCRETE

M A R Bhutta*, University Teknologi Malaysia, Malaysia

K Tsuruta, Materras Oume Concrete Industry, Ltd., Japan

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35th Conference on OUR WORLD IN CONCRETE & STRUCTURES: 25 27 August 2010, Singapore

EVALUATION OF PROPERTIES OF WORKABLE POROUS CONCRETE

M A R Bhutta*, University Teknologi Malaysia, Malaysia K Tsuruta, Materras Oume Concrete Industry, Ltd., Japan

Abstract This paper presents a laboratory study conducted to evaluate the properties of workable porous concrete having good workability and cohesiveness; no segregation or bleeding; requires no special vibration equipment and curing, and develops high strength. The optimum mix proportions using three sizes of coarse aggregates with appropriate amount of high water-reducing and thickening (cohesive) agents were used in the preparation of workable porous concretes and investigated for the evaluation of properties such as slump, slump-flow, void ratio, coefficient of permeability, flexural and compressive strengths. In addition, a self-compaction test was proposed by authors to determine the effects of the thickening (cohesive) and high water-reducing agents on self-compaction of workable porous concrete on its hardened properties from the viewpoint of practical application. The strength development of workable porous concretes was also examined at curing period of 1, 3, 7, 14 and 28 days at 20 and 60% RH. Consequently, workable porous concrete exhibited good workability, no segregation or bleeding and provides high strength development compared to conventional porous concrete. The results of self-compaction test for workable porous concrete also show good workability and cohesiveness without any special compaction or vibration. Keywords: Workable porous concrete; self-compaction; coefficient of permeability; compressive and flexural strengths; strength development; total void ratio.

1. Introduction

Porous concrete has been developed as an environmentally friendly material in Japan in the 1980s. Since then it has been widely used in various applications in Japan, USA and Europe because of its multiple environmental benefits such as controlling storm water runoff, restoring groundwater supplies, and reducing water and soil pollution [1-6]. The water-permeating, water-draining, and water retaining performances of the porous concrete have been utilized in road pavements, sidewalks, parks, and building exteriors, as well as for plant bedding and permeable rainwater retention facilities, such as permeable trenches, permeable gullies and permeable gutters. In general, a gap-graded conventional porous concrete (CPC) or no fines concrete, where the fine aggregate is omitted entirely and a uniform size of coarse aggregate is used with low water-cement ratio less than 30%, shows poor workability, needs vibration equipment for proper compaction and curing for the production of precast products, and for drainage pavement application. The research significance of this paper is that it evaluates the properties of developed workable porous concrete (WPC) which has good workability and cohesiveness to fill the spaces of almost any size and shape without segregation or bleeding; requires no special

vibration equipment and curing, and develops high strength [7,8]. The optimum mix proportions of WPC using different coarse aggregate size and appropriate amount of high water-reducing and thickening (cohesive) agents were mixed and examined the applicability of WPC from the view point of practical application in place of CPC conducting the tests: slump, slump-flow; total void ratio; coefficient of permeability; flexural strength and compressive strengths. A self-compaction test for WPC was proposed by authors to determine the effect of the thickening (cohesive) and high water-reducing agents on self-compaction of workable porous concrete on its hardened properties from the viewpoint of practical application. As a result, the porous concrete exhibits good workability, no segregation or bleeding and provides high strength compared to CPC.

2. Materials

Ordinary portland cement and commercially available high water-reducing agent (density: 1.06 g/cm3), and thickening (cohesive) agent (water-soluble polymer as powder, cellulose type, density: 2.40 g/cm3) were employed for the preparation of cement pastes, and three types of crushed coarse aggregates No.5 (1320mm); No.6 (513mm) and No.7 (2.55mm) were used in the preparation of all porous concretes.

3. Testing Procedures 3.1 Preparation of Specimens

Porous concretes were mixed according to the mix proportions shown in Tables 1 and 2. Specimens were prepared according to JIS Method of Making Porous Concrete Specimens (draft) for total void ratio measurement, coefficient of permeability test, compressive and flexural strengths. Concrete mixing was done at room temperature (20 ) and specimens were kept at the same temperature for 1-day. After demolding, the specimens were placed at 20 and 60% RH for 28 days.

Table 1. Mix proportions of WPC concretes.

Note; Ad. I: High water-reducing agent, Ad. II: Thickening (cohesive) agent Table 2. Mix proportions of CPC concrete.

3.2 Slump and Slump-Flow Test In accordance with JIS A 1101 (Method of Test for Slump of concrete) and JIS A 1150 (Method of Test for slump-flow of concrete), slump and slump-flow tests were conducted. 3.3 Flexural and Compressive Strength Tests The flexural (101040cm) and compressive (1020cm) strengths were performed according to JIS A 1106 (Method of Test for Flexural Strength of Concrete) and JIS A 1108 (Method of Test for Compressive Strength of Concrete). 3.4 Total Void Ratio Measurement Test JCI Test Method (Report on Eco-Concrete Committee) for Void Ratio of Porous Concrete (draft) was used to determine the total void ratio of porous concrete (1020cm). The total void ratio was obtained by dividing the difference between the mass (M1) of the cylinder specimen (1020 cm) in the water and

Aggregate size W/C (%) Ad.

I Ad. II

Mix proportions, (kg/m3) W C G Ad.I Ad.II

No.5 (1320mm) 30 1.0 0.60 99 300 1500 3.00 1.80 No.6 (513mm) 30 1.0 0.26 111 370 1398 3.70 0.96 No.7 (2.55mm) 35 1.1 0.15 138 395 1390 4.35 0.60

Aggregate size W/C (%) Mix proportions, (kg/m3)

W C G No.5 (1320mm) 27 85 320 1620

No.6 (513mm) 27 70 260 1800 No.7 (2.55mm) 30 89 300 1640

that (M2) measured following air drying for 24 hours with the specimen volume. The equation used to obtain total void ratio (A) is as follows:

V

MMA )12(1(%) 100

3.5 Coefficient of Permeability Test According to JCI Test Method for Permeability of Porous Concrete (draft), the coefficient of permeability of porous concrete (1020cm) was determined. 3.6 Strength Development Test To examine the strength development of WPC and CPC, specimens 1020cm for compressive strength and 101040cm for flexural strength, were prepared according to the JCI Method of Making Porous Concrete Specimens (draft). These specimens were cured for 1, 3, 7, 14 and 28 days at 20 and 60% RH. 3.7 Self-Compaction Test To examine the self-compaction of WPC, authors proposed a simple test method. A diagram of a mold is demonstrated in Fig.1. Only two types of coarse aggregates of No.6 (513mm) and No.7 (2.55mm) were employed in mix proportions of WPC. Self-compaction of WPC was tested by freely dropping the porous concrete into PVC pipe (10100cm) mold as shown in Fig. 1. After demolding and preparing specimens, the apparent density, total void ratio, coefficient of permeability and compressive strength of WPC specimens were calculated. Apparent density was calculated as follows using the following equations: Apparent density (g/cm3) = (1)

Compaction index was calculated by the following equation: Compaction index (%): (D1 / D2) 100 (2) where D1 is apparent density of porous concrete placed by freely dropping porous concrete into mold and D2 is apparent density of porous concrete placed into molds according to the JCI Method of Making Porous Concrete Specimens (draft). Concrete mixing was done at room temperature and specimens were kept at the room temperature for 1-day. The specimens were placed at 20 and 60% RH for 28 days. Fig. 1 A simple diagram of PVC mold.

10cm

Steel Plate

Height: 100 cm

80100cm

5070cm

3050cm

20cm

Cutting

Cutting

Bottom

First from top

Top most

Second from top

Porous Concrete

PVC Pipe

Volume of the specimen Mass of the specimen

4. Test Results and Discussion 4.1 Slump and slump-flow Table 3 presents a comparison between the properties of CPC and WPC. Generally, CPC is a special type of gap-graded concrete, where the fine aggregate is omitted entirely and a uniform size of coarse aggregate is used with low water-cement ratio, therefore, CPC shows very poor workability. As shown in Table 3 and Fig. 2, WPC exhibits good workability almost at the same void ratio as compared to that of CPC. The improvement in workability is due to appropriate amounts of high water-reducing and thickening agents in optimum mix proportions of WPC. Table 4 shows evaluation performance for workability of WPC and CPC. Table 3 Properties of CPC and WPC (Comparison).

Table 4 Evaluation performance for workability

Evaluation performance for workability WPC CPC

Mixability Excellent Fair Flowability Good Poor Placability Good Poor Compactability Good Poor Finishability Excellent Poor Totals remarks Excellent Poor

4.2 Total void ratio, Compressive and Flexural strengths Figs. 3 and 4 show the effect of aggregate size on total void ratio, compressive and flexural strengths of all porous concretes, and the effect of thickening (cohesive) agent on strength of WPC. In general, aggregate gradation exhibited significant effect on the total void ratio. The total void ratio is decreased with decreasing aggregate size. It is seen that most of the porous concretes had total void ratio within the range from 18 to 28% regardless of aggregate size, which is acceptable. Moreover, the addition of thickening agent (cohesive) resulted in a further slight decrease in total void ratio of WPC. In the modification with water-soluble polymer as powder to cement paste during mixing, improves the workability because of the surface activity and increase the viscosity of water phase in the modified cement paste due to the formation of very thin and water-impervious film in the paste [9]. With the increase in the viscosity of cement paste, the volume of cement paste is also increased decreasing the

Item CPC WPC

(1) Poor workability Good workability (2) No cohesiveness Cohesiveness (3) No self compaction Self-compaction (4) Vibration is required No vibration (5) Void ratio: 1825% Void ratio: 1825% (6) Low strength High strength (7) Steam curing No curing

CPC WPC

Fig. 2 Slump and slump-flow of CPC and WPC.

pores made between the aggregates. As expected, the smaller the coarse aggregate size, the higher the strengths. It is evident that the compressive and flexural strengths of WPC are higher than those of CPC. It is believed that the bonding force of cement matrix to aggregates was improved by adding thickening (cohesive) agent in mix proportions of WPC. The addition of thickening (cohesive) agent to WPC increase the workability of cement paste which overlaps aggregates well and thus increases the contact area between neighboring aggregate particles. Subsequently, the increased contact area will result in strength improvement. More importantly, the thickening (cohesive) agent and the cement hydration products co-mingle and create two interpenetrating matrices which work together, resulting in improved strength.

Fig. 4 Effect of aggregate size on flexural and compressive strengths of porous concretes.

Fig. 3 Effect of aggregate size on total void ratio of porous concretes.

Fig. 5 Effect of aggregate size on coefficient of water permeability of porous concretes.

4.3 Coefficient of Permeability Fig. 5 exhibits the effect of aggregate size on coefficient of permeability of all porous concretes as well as the effect of thickening (cohesive) agent on permeability of WPC. It is evident from Fig. 5 that all the porous concretes show permeability values between 0.25 to 3.3 cm/s, which is high enough to be used as a drainage layer for pavement structures or for porous concrete blocks. The aggregate gradation did not show consistent influence on the permeability. According to Fig. 5, the effect of thickening (cohesive) agent on permeability was similar to that on total void ratio of WPC. Although the addition of thickening (cohesive) agent could lead to a reduction in permeability, the permeability value was comparable and acceptable compared to the general requirement of drainage. 4.4 Strength development Fig. 6 represents the effect of curing period on compressive and flexural strengths of WPC and CPC. In general, the compressive and flexural strengths of WPC and CPC increase gradually till a curing period of 14 days and become almost constant at a curing period of 28 days. WPC show high strength development in compression and flexural than that of CPC at same curing period. The addition of thickening (cohesive) agent in cement binder significantly affects the properties of WPC. The cement binder becomes cohesive with no bleeding or segregation. The cohesiveness of cement paste due to thickening (cohesive) agent along with high water-reducing agent in WPC makes it satisfactory as workable porous concrete. The addition of thickening (cohesive) agent in the mix proportions of WPC successfully produced high-strength porous concrete with low total void ratio compared to CPC. 4.5 Effect of Freely Dropping Method of WPC on Self-Compaction The results are given in Tables 5 and 6, and in Figs. 7 and 8. Table 5 shows slump and slump-flow of WPC using No.6 and No.7 aggregates. The workability of WPC is evident. Tables 5 exhibits the apparent density of WPC specimens prepared by freely dropping method. The apparent density of specimens is almost the same due to good workability of WPC that could fill the spaces of almost any size and shape. The effect of the freely dropping method on fresh and hardened properties of porous concretes are depicted in Figs. 7 and 8. It can be observed that apparent density, compaction, total void ratio, coefficient of permeability, compressive strength are quite influenced by the freely dropping method. In general, the apparent density, compaction, total void ratio, coefficient of permeability, and compressive strength of specimen taken from bottom of porous concrete poles are somewhat higher than those of specimens taken from center or upper positions due to the compaction provided by freely dropping porous concrete mass. The compressive strengths of WPC at bottom to top most positions are higher than 10 N/mm2 which is required in stone revetment application. The apparent density and compaction decreased with the use of the freely dropping porous concrete and eventually total void ratio is increased. That means large porosity or voids are developed which caused a decrease in compressive strength of WPC. However, the purpose of evaluating the self-compaction of WPC doing this experiment is achieved and it can be concluded that WPC can be used effectively in heavy stone revetment, revetment of porous concrete blocks along with banks of river and revetment of water purifying porous concrete blocks without using any vibration equipment. It should be noted that WPC is a porous concrete and it contains

Fig. 6 Effect of different curing period on compressive and flexural strengths development.

less cement binder and high amount of aggregate, therefore, it must need some compaction by the tamping method regarding application or should be prepared according to the JCI Method of Making Porous Concrete Specimens (draft).

Fig. 7 represents the compaction index vs. position of specimen of WPC. The effect of thickening (cohesive) agent on self-compaction of WPC is noticeable. Regardless of the position of specimen and aggregate size, the compaction index of specimens is more than 80%, which means that the WPC showed good workability and cohesiveness due to appropriate amount of thickening (cohesive) agent and high water-reducing agent to make porous concrete workable enough to fill the spaces of almost any size and shape without segregation or bleeding. Fig. 8 exhibits the effect of total void ratio on compressive strength of WPC specimen at different

Type of Aggregate Slump (cm)

Slump-flow (cm)

No.6 (513mm) 22.2 43 No.7 (2.55mm) 20.5 46

Type of Aggregate

Apparent density (g/cm3)

Top most First from Top Second from Top Bottom

No.6 (513mm) 1.73 1.67 1.62 1.62

No.7 (2.55mm) 1.74 1.72 1.70 1.70

Table 6 Apparent density of WPC specimens.

Table 5 Slump and slump-flow of WPC.

Fig. 8. Compressive strength and total void ratio vs. position of specimen. Note, *: Total void ratio

Fig. 7 Compaction index vs. position of specimen.

positions. As discussed above, that the freely dropped mass of porous concrete itself has great influence on total void ratio and compressive strength. All porous concrete specimens from top most position to bottom position have total void ratio of more than 23 to 32% which is relatively larger than that of porous concrete specimens prepared according to JCI method. However, all porous concrete specimens from top most to bottom position showed more than 10MPa compressive strength which is required in the applications of drainage pavement, stone revetment and the production of precast porous concrete products. The reason for high compressive strength in spite of large total void ratio is good workability achieved by the thickening (cohesive) agent and the cement hydration products co-mingle and create two interpenetrating matrices which work together, resulting in improved strength.

The permeability results as well as the effects of the self-compaction due to thickening (cohesive) agent and freely dropping method on permeability of WPC are shown in Fig. 9. It is seen in the Fig. 9 that all porous concrete specimens showed permeability values between 0.9 to 3.1 cm/s which is acceptable as a stone revetment application. The aggregate gradation and position of specimens have a consistent influence on permeability of porous concretes. WPC made with different size aggregates exhibited different permeability values.

5. Conclusions

A laboratory experiment was conducted to investigate the total void ratio, permeability and strength properties of workable porous concretes. The effects of aggregate gradation and thickening (cohesive) agent evaluated based on the laboratory test results. Based on this study, the following conclusions can be drawn:

1) Use of the combination of thickening (cohesive) agent and high water-reducing agent could produce acceptable porous concrete with good workability, enough drainage and strength properties.

2) The addition of thickening (cohesive) agent to porous concrete mix could decrease the total void ratio and permeability and significantly increase the compressive and flexural strengths.

3) The effect of aggregate gradation on total void ratio, permeability and strength properties is evident.

4) The evaluation of workability of WPC by freely dropping method is successfully determined. The apparent density of WPC at different positions is almost the same and WPC showed compaction index more than 80%. The permeability of WPC by freely dropping method is acceptable, however, WPC made with different size aggregates exhibited different permeability values.

WPC is superior in strength and cohesive properties to CPC. It exhibits the ability of resist segregation, ease of compaction and suitable strength. It can be successfully employed in the applications of drainage pavement, stone revetment and the production of precast porous concrete products.

Fig. 9 Effect of position of specimen on coefficient of permeability.

Acknowledgements The authors wish to express their sincere appreciation to Research and Development Center, Takamura Holdings Co. for financing this research work and conducting experiments in its laboratory.

6. References [1] M.Tamai, H.Mizuguchi, S.Hatanaka, H.Katahira, T.Nakazawa, K.Yanagibashi and M.Kunieda, Design, Construction and Recent Applications of Porous Concrete in Japan, Proceedings of the JCI Symposium on Design, Construction and Recent Applications of Porous Concrete, Japan Concrete Institute, April, 2004, pp.1 to 10, Tokyo. [2] A. Beeldens, Influence of Polymer Modification on the Behavior of Concrete under Severe Conditions, PhD dissertation, Faculty of Engineering, Katholieke Universiteit Leuven, Belgium, 2002, pp. 248. [3] A. Beeldens, D. Van Gemert, C. Caestecker, M. Van Messem, Mechanical Properties and Structure of Porous Concrete, Proceedings of the 8th International Symposium on Concrete Roads, Lisbon, 1998, pp. 129-134. [4] F. Monters, Pervious Concrete: Characterization of Fundamental Properties and Simulation of Microstructure, PhD dissertation, University of South Carolina, 2006. [5] S. Kajio, S. Tanaka, R. Tomita, E. Noda, and S. Hashimoto, Properties of Porous Concrete with High Strength, Proceedings of the 8th International Symposium on Concrete Roads, Lisbon, 1998, pp. 171-177. [6]W. Wang, Study of Pervious Concrete Strength, Sci Technology Build Mater China, 1997, 6(3), 25-8. [7] M.A.R.Bhutta and K.Tsuruta, A Study on the Application of Porous Concrete Pavement, Proceedings of the International Conference on Advances in Cement Based Materials and Applications in Civil Infrastructure (ACBM-ACI), University of Engineering and Technology, Lahore, Pakistan, Dec. 12-14, 2007, 743-752. [8] M.A.R.Bhutta, K.Tsuruta and S.Takamura, Evaluation of Basic Properties of Flowable Porous Concrete, Proceedings of the Eighth International Summer Symposium, International Activities of Committee, Japan Society of Civil Engineers, Nagoya University, Nagoya, July 29, 2006, pp.303-306. [9] Y. Ohama, Handbook of Polymer-Modified Concrete and Mortars: Properties and Process Technology, Noyes Publications, New Jersey, 1995.