Self Compacted Concrete Essay

Shamsad Ahmad, Abul Kalam Azad, and Mohammed Abdul Hameed A STUDY OF SELF-COMPACTING CONCRETE MADE WITH MARGINAL AGGREGATES Shamsad Ahmad? , Abul Kalam Azad, and Mohammed Abdul Hameed Department of Civil Engineering King Fahd University of Petroleum & Minerals Dhahran, Saudi Arabia 1. INTRODUCTION Self-compacting concrete (SCC), developed first in Japan in the late 1980s, represents one of the most significant advances in concrete technology in the last two decades.

SCC was developed to ensure adequate compaction through self-consolidation and facilitate placement of concrete in structures with congested reinforcement and in restricted areas. SCC can be described as a high performance material which flows under its own weight without requiring vibrators to achieve consolidation by complete filling of the formworks even when access is hindered by narrow gaps between reinforcement bars [1]. The high flowability of SCC makes it possible to fill the formwork without vibration [2].

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The constituent materials used for the production of SCC are the same as those for conventionally vibrated normal concrete except that SCC contains a lesser amount of aggregates and larger amount of powder (cement and filler particles smaller than 0. 125 mm) and special plasticizer to enhance flowability. Fly ash, glass filler, limestone powder, silica fume, etc. are used as the filler materials. High flowability and high segregation resistance of SCC are obtained by using: (i) a larger quantity of fine particles, i. e. limited aggregate content (coarse aggregate: 50% of the concrete volume and sand: 40% of the mortar volume) [3]; (ii) a low water/powder ratio; and (iii) a higher dosage of superplasticizer and stabilizer [4, 5]. Stabilizer is needed for SCC mixes for maintaining proper cohesiveness so that highly flowable SCC would not segregate. Typical ranges of proportions and quantities of the constituent materials for producing SCC are reported in the literature [2, 6–9]. Relevant information regarding design of SCC mixtures is reported by Su et al. [6], Patel et al. [10] and Sonebi [11 and 12].

Various tests for assessment of compactibility and flowability are described by EFNARC [7]. The strength of SCC has been reported by many researchers [10, 13–15]. The bond behavior of SCC was found to be better than that of normally vibrated concrete [16]. A relatively low modulus of elasticity can be expected, because of the high content of ultra fines and additives as dominating factors and, accordingly, minor occurrence of coarse and stiff aggregates at SCC [17, 18]. Shrinkage and creep of the SCC mixtures have not been found to be greater than those of traditional vibrated concrete [9, 19, and 20].

Studies on durability characteristics of SCC, namely, water absorption, initial surface absorption, water permeability, and chloride permeability, have shown that SCC has either performed better or same as the normal concrete [9, 10, 21] ? Address for correspondence: PO Box 1403 King Fahd University of Petroleum & Minerals Dhahran-31261, Saudi Arabia Fax: 966-3-8602879 E-mail: [email protected] edu. sa Paper Received 25 June 2007; Revised 21 January 2008; Accepted 22 March 2008 October 2008 The Arabian Journal for Science and Engineering, Volume 33, Number 2B 37 Shamsad Ahmad, Abul Kalam Azad, and Mohammed Abdul Hameed In view of the fact that SCC has not yet made any inroad into Saudi Arabia’s construction industry, this study was undertaken with the aim to shed some informative data on SCC made from locally available aggregates. Most of the coarse aggregates available in the eastern region of Saudi Arabia are crushed tertiary age weaker dolomitic limestone. As the aggregates are porous, highly absorptive, relatively soft, and excessively dusty, they can be classified as “marginal”.

The aeolian dune sands in the coastal areas form the main source of fine aggregate. These sands are essentially fine grained and have narrow grading with excessive dust. Nearly all the material passes No. 30 sieve and an appreciable portion, 10 to 20%, passes # 100 sieve. Both coarse and fine aggregates from local sources can be characterized as marginal, as their properties do not meet the standards of sound quality. This study explores the use of local marginal aggregates in producing SCC that has reasonable strength and no short-term durability implications.

The findings of this study may encourage further research and possible adoption of SCC in local construction. 2. EXPERIMENTAL PROGRAM 2. 1. Composition of Trial Mixes and Their Properties For selecting a suitable mix using local marginal aggregates, trial mixes were considered by varying the mix parameters, such as quantity of filler and superplasticizer and fine aggregate/coarse aggregate ratio, while keeping the water/powder ratio constant. The specific gravity of Type I cement used was taken as 3. 15 as per the product information available from the manufacturer.

The coarse aggregates used in this study were crushed limestone processed from the local quarries in Abu Hadriah, Saudi Arabia. The maximum aggregate size was 20 mm and the grading of coarse aggregates used corresponds to ASTM C 33 (size number 7) [22]. The average values of specific gravity and absorption of the coarse aggregate, determined in accordance with ASTM C 127 [23], were 2. 5 and 1. 5%, respectively. Local dune sand was used as fine aggregate. The specific gravity and absorption of the fine aggregate were typically 2. 6 and 0. 57%, respectively.

A highly pulverized fly ash commercially known as Super-pozz® [24] was used as a filler. The specific gravity of Super-pozz® [24] used in this study was 2. 15. Superplasticizer by the trade name of Structuro 220 was used. The specific gravity of the superplasticizer as given by the supplier is 1. 08 and the pH is 6. 5 with chloride content of less than 0. 1%. A high performance commercially available cohesion agent Structuro 420, specially designed to ensure a good consistency and stability in concrete with very high fluidity, was used as a stabilizer.

The specific gravity of Structuro 420 as specified by the supplier is 1. 01. Eight trial mixes were prepared by using a fixed amount of cement (350 kg/m3) and varying the Super-pozz® [24] content, fine to coarse aggregate ratio, and superplasticizer content to select a suitable mix. Two levels of the Superpozz® [28] 100 and 125 kg/m3, two levels of fine to coarse aggregate ratio: 1 and 1. 1 (by mass), and two levels of superplasticizer (Structuro 220): 0. 8 and 1. 0% (by mass of powder) were used for preparing and testing eight trial mixes. For each trial mix, a constant water/powder ratio of 0. 8 (by mass) and a constant amount of stabilizer (Structuro 420) 3. 03 kg/m3 of concrete were taken. Proportioning of the trial mixes was carried out using the absolute volume method [25]. Quantities of the ingredients calculated for all eight trial mixes of SCC (TM1 through TM8) are presented in Table 1. Table 1. Weights of Constituents in Trial Mixes of SCC Trial Mix # TM1 TM2 TM3 TM4 TM5 TM6 TM7 TM8 Mix Variables FA/CA ratio 1 1 1 1 1. 1 1. 1 1. 1 1. 1 Filler content (kg/m3) 100 100 125 125 100 100 125 125 Structo 220 (%) 0. 80 1. 00 0. 80 1. 00 0. 80 1. 0 0. 80 1. 00 Water 190. 0 189. 6 198. 7 198. 1 189. 4 188. 9 198. 0 197. 4 Filler 100 100 125 125 100 100 125 125 Quantities of Mix Ingredients (kg/m3) Powder Cement 350 350 350 350 350 350 350 350 FA 846 846 819 819 888 888 859 859 CA 846 846 819 819 807 807 781 781 Str. 220 3. 6 4. 5 3. 8 4. 7 3. 6 4. 5 3. 8 4. 7 Str. 420 3. 03 3. 03 3. 03 3. 03 3. 03 3. 03 3. 03 3. 03 Density 2339 2339 2318 2318 2341 2341 2319 2320 438 The Arabian Journal for Science and Engineering, Volume 33, Number 2B October 2008 Shamsad Ahmad, Abul Kalam Azad, and Mohammed Abdul Hameed

Each of the eight trial mixes was prepared and tested for self-compactibility and compressive strength. TM6 of the eight trial mixes, TM1 – TM8, satisfies the self-compactibility criteria given in reference [7] and has 28-d strength more than other six trial mixes. It was therefore selected as the most suitable SCC mix in this study. Fresh and hardened properties of the selected mix are listed in Table 2. For each test conducted on fresh and hardened concrete samples three replicate samples were tested and the average of the three test results was reported.

Table 2. Properties of the Selected SCC Mix (TM6) Property Flow table value [26] Recommended range: 650 to 800 mm [7] V-funnel value [27] Recommended range: 6 to 12 sec [7] U-tube value [28] Recommended range: 0 to 30 mm [7] 28-d compressive strength [29] 2. 2. Exposure Tests for the Selected SCC Mix To study the effect of wet–dry and heat–cool cyclic exposures on hardened properties of the selected SCC mix, the specimens after 28 days of moist curing were exposed to normal laboratory, heat–cool and wet–dry exposures for a period of four months.

Exposure to room temperature in laboratory was considered as normal. Heat–cool cyclic exposure consisted of heating the specimens in oven at 40°C for 2 days and then cooling them at room temperature for 2 days. Wet–dry cyclic exposure consisted of wetting the specimens using water for 2 days and then drying them in an oven at 30°C for 2 days. The cyclic exposure conditions were designed to account for the damaging impact of heat–cool and wet–dry cycles, if any, on the performance of the SCC samples in a short period of time.

After completion of the cyclic exposure regimes, specimens were tested for compressive strength [29], rapid chloride permeability [30], water absorption [31], depth of water penetration [32], and water permeability [33]. Additionally, drying shrinkage was also monitored over a period of about 90 days [34]. 3. RESULTS AND DISCUSSION The results for compressive strength, rapid chloride permeability, water absorption, depth of water penetration, and water permeability obtained from tests conducted on samples after about four months of exposure are presented in Table 3.

Compared to the 28-day compressive strength of 41. 5 MPa, the average compressive strength of the specimens subjected to normal exposure is higher about 12%. This is due to the age effect. Further, compared to the compressive strength of concrete specimens exposed to normal conditions, the compressive strengths of specimens exposed to wet– dry and heat–cool conditions were higher by about 6% and 14%, respectively. It should be noted that all specimens, whose test results are presented in Table 3, were moist cured for 28 days and then were subjected to normal, wet–dry and heat–cool cycles, as mentioned earlier.

At the time of testing the specimens under wet–dry and heat–cool cycles were relatively much drier than those tested under normal exposure. The small increase in compressive strength of SCC specimens exposed to wet–dry and heat–cool conditions compared to those exposed to normal conditions may therefore be attributed to moisture effect on compressive strength. However, it is expected that, like normal compacted concrete, the compressive strength of SCC will be adversely impacted by a prolonged wet–dry or thermal cycles.

Table 3. Results of Tests Conducted After About Four Months of Exposures Property Compressive strength (MPa) Water absorption (%) Depth of water penetration (mm) Water permeability (m/s) Chloride permeability (Coulombs) Tested values for different exposure conditions Normal laboratory exposure 46. 5 3. 51 37 13. 1? 10 438 –12 Measured value 720 mm 10 s 5 mm 41. 5 MPa Wet–dry Cycles 49. 5 3. 18 24 6. 3? 10 782 –12 Heat–cool cycles 52. 9 4. 44 40 12. 7? 10–12 522 October 2008

The Arabian Journal for Science and Engineering, Volume 33, Number 2B 439 Shamsad Ahmad, Abul Kalam Azad, and Mohammed Abdul Hameed The water absorption in the specimens exposed to wet–dry condition was less than that in the specimens exposed to normal conditions by about 9%. The water absorption of specimens exposed to heat–cool conditions, however, was more than that of specimens exposed to normal conditions, by about 26%, reflecting the detrimental effect of thermal cycling on water absorption.

The depth of water penetration measured in the wet–dry cycled specimens when tested in DIN 1048 [32] water permeability tests corresponds to the “low permeability” and that for specimens exposed to normal and heat–cool conditions corresponds to “moderate permeability”, according to the criteria set by the Concrete Society [35]. The depth of water penetration in the specimens exposed to wet–dry conditions is 35% less than that in the specimens exposed to normal conditions, while that in the specimens exposed to heat–cool conditions is slightly higher.

The reduction in the depth of water penetration in the specimens exposed to wet–dry conditions may be attributed to the effect of intermittent curing. Limited wet–dry cycles seem to improve water-tightness of SCC specimens, confirming further the results observed in absorption tests. Heat–cool cycles have shown the trend of increasing the depth of water penetration as well as the water absorption. It is expected that a prolonged cycle will result in higher depth of water penetration. In each case of the cyclic testing, the water permeability is found to be lesser than the maximum permissible value of the water permeability coefficient (15? 0? 12 m/s) for a conventional concrete, recommended by ACI 301 [36]. Similar to the depth of water penetration, the coefficient of water permeability for the specimens exposed to wet–dry conditions was about 50% less than that for specimens exposed to normal conditions. The coefficient of water permeability for specimens exposed to normal and heat–cool conditions was almost similar. The decrease in the coefficient of water permeability in the SCC specimens exposed to wet–dry conditions may be attributed to the effect of intermittent curing.

The chloride permeability for all the specimens was “very low”, according to ASTM C 1202 [30] criteria. The chloride permeability values obtained for all three exposures fall well within the range of rapid chloride permeability value of SCC reported recently in literature [10–15]. The rapid chloride permeability results should not be treated strictly in terms of the amount of the charges (coulombs) but as measure of a qualitative ranking for permeability. In this sense, all specimens under different exposure conditions are ranked equal for chloride permeability.

The shrinkage strains measured for SCC in the present study and reported in some of literature are presented in Table 4. Table 4. Shrinkage Data for SCC Source Present study Xie et al. [14] Bouzoubaa and Lachemi [37] Shrinkage strain (in ? 10–6) 486 to 608 after 90 days 383 after 90 days 493 to 591 after 112 days Xie et al. [14] have reported that the 90 days drying shrinkage of SCC was 383 ? 10–6, which is less than the values obtained under the present study. This is because of differences in the mix proportions, admixture type and dosage, and specimen size.

This study shows no detrimental effect of the limited cyclic exposures on the durability of SCC, pointing to a durable product of adequate strength. This signals an encouragement to its adoption in local concrete construction. However, clearly there is a need for a long-term durability study under various exposure conditions to verify if there is any longterm durability concern for SCC compared to normal compacted concrete. 4. CONCLUSIONS The primary aim of this research was to design a suitable SCC mix with local aggregates and thereafter determine its durability under limited cycles of wet–dry and thermal exposures.

The main conclusions drawn from the results are listed below: 1. From several trial mixes of SCC, it has been shown that a suitable mix of adequate compressive strength can be formulated with local marginal aggregates by using a FA/CA ratio of 1. 1, cement content of 350 kg/m3 and Superpozz in the amount of 100 kg/m3 that would satisfy the flowability and compactivity criteria. The limited exposure period considered in this study has not led to any significant degradation of durability of SCC under repeated wet–dry and heat–cool cycles. It appears that under such cyclic environment, the . 440 The Arabian Journal for Science and Engineering, Volume 33, Number 2B October 2008 Shamsad Ahmad, Abul Kalam Azad, and Mohammed Abdul Hameed durability of SCC made with local marginal aggregates will not be worse than that of a comparable, vibrated normal concrete. 3. Producibility of SCC with local marginal aggregates that has adequate strength and its durability unaffected by limited cyclic exposures is an encouragement to its adoption. Understandably, a long-term durability assessment is essential to reaffirm the initial findings to lend further confidence in this product.

ACKNOWLEDGMENTS The authors gratefully acknowledge the financial support received under the research grant FT/2004-24. The support of the Department of Civil Engineering at KFUPM is also acknowledged. REFERENCES [1] [2] [3] [4] [5] [6] [7] [8] [9] W. Zhu, C. J. Gibbs, and P. J. M. Bartos, “Uniformity of In Situ Properties of Self Compacting Concrete in Full-scale Structural Elements”, Cement & Concrete Composites, 23(2001), pp. 57–64. K. H. Khayat, J. Assaad, and J. Daczko, “Comparison of Field-Oriented Test Methods to Assess Dynamic Stability of Self-Consolidated Concrete”, ACI Materials Journal, 101(2)(2004), pp. 68–176. H. Okamura and K. Ozawa, “Mix Design for Self-Compacting Concrete”, Concrete Library of JSCE, 25(1995), 107–120. pp. H. Okamura and M. Ouchi, “Self-Compacting Concrete”, Journal of Advanced Concrete Technology, 1(1)(2003), pp. 5–15. K. Audenaert, V. Boel, and G. D. Schutter, “Carbonation of Self Compacting Concrete”, 6th International Symposium on High Strength/High Performance Concrete, Leipzig, June, 2002, pp. 853–862. N. Su, K. C. Hsu, and H. W. Chai, “A Simple Mix Design Method for Self-Compacting Concrete”, Cement and Concrete Research, 31(2001), pp. 799–1807. EFNARC, “Specifications and Guidelines for Self-Compacting Concrete,” EFNARC, UK (www. efnarc. org), February, 2002, pp. 1–32. C. Munn, “Self Compacting Concrete (SCC): Admixtures, Mix Design Consideration and Testing of Concrete”, Technical Paper Presented in the Meeting of the ACI, Saudi Arabia Chapter, Eastern Province, October 2003. Y. P. Kapoor, C. Munn, and K. Charif, “Self-Compacting Concrete – An Economic Approach”, 7th International Conference on Concrete in Hot & Aggressive Environments, Manama, Kingdom of Bahrain, 13–15 October, 2003, pp. 09–520. R. Patel, K. M. A. Hossain, M. Shehata, N. Bouzoubaa, and M. Lachemi, “Development of Statistical Models for Mixture Design of High-volume Fly Ash Self-consolidating Concrete”, ACI Materials Journal, 101(4)(2004), pp. 294–302. M. Sonebi, “Applications of Statistical Models in Proportioning Medium-Strength Self-Consolidating Concrete”, ACI Materials Journal, 101(5)(2004), pp. 339–346. M. Sonebi, “Medium Strength Self-compacting Concrete Containing Fly Ash: Modeling Using Factorial Experimental Plans”, Cement and Concrete Research, 34(2004), pp. 1199–1208. W.

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