CC BY-NC-ND
0Available online at www.sciencedirect.com
ScienceDirect
Procedía Engineering
ELSEVIER
ProcediaEngineering 14(2011) 805-813
www.elsevier.com/locate/procedia
The Twelfth East Asia-Pacific Conference on Structural Engineering and Construction
Self Compacting Concrete (SCC) is new type of concrete that posse's property of high flow ability, passing ability and stability. To achieve SCC, many factors must be investigated. Coarse aggregate is one of these factors that have a significant influence on SCC. This paper presents the coarse aggregate properties such as maximum size, texture and type of coarse aggregate that have a direct effect on achieving SCC. Three types of coarse aggregate are used, namely crush gravel, uncrushed gravel and crush limestone. To determine the workability, different test methods are adopted such as slump flow, V-funnel, L-box and U-box test. It was found that by increasing the maximum size of coarse aggregate, flowability and passing ability reduced. In addition it was observed that when uncrushed gravel was used in the concrete mixture, flow ability, passing ability and segregation resistance increased as compared to concrete with crushed gravel. Furthermore, the inclusion of 10% HRM as a partial replacement by weight of cement leads to reduce flow ability and increase viscosity. The compressive and flexural strengths and modulus of elasticity was measured. It was noticed that concrete mixes prepared with crushed limestone showed higher strengths and modulus of elasticity than concrete mixes prepared with crushed and uncrushed gravel. In addition, lower maximum size of coarse aggregate leads to higher strengths compared to higher maximum size of coarse aggregate in SCC mixes.
© 2011 Published by Elsevier Ltd.
Keywords: Limestone aggregate, gravel aggregate, maximum size, texture, Self compacting concrete properties.
a Corresponding author: Email: omar.engineer.ct@gmail.com a Presenter: omar.engineer.ct@gmail.com
The Effect of Coarse Aggregate on Fresh and Hardened Properties of Self-Compacting Concrete (SCC)
O. R. KHALEEL1a, S. A. Al-MISHHADANI2, and H. Abdul RAZAK1
1 Department of Civil Engineering, Faculty of Engineering, University of Malaya, Malaysia
2 Department of Building and Construction, University of Technology, Iraq 3 Department of Civil Engineering, Faculty of Engineering, University of Malaya, Malaysia
Abstract
1877-7058 © 2011 Published by Elsevier Ltd. doi:10.1016/j.proeng.2011.07.102
1 INTRODUCTION
In concrete technology, self-compacting concrete (SCC) is considered to be one of the most important innovations. It is a highly workable concrete that can flow through congested reinforcing under its own weight and sufficiently fill voids without tending to segregation or excessive bleeding and without the need for vibration to consolidate it. The aggregates, which form more than 60% of the volume of concrete, play a main role in affecting its fresh as well as hardened properties. SCC is very sensitive to changes in aggregate characteristics (shape, texture, maximum size, grading and morphology), so the aggregate should be chosen carefully before using it in SCC.
As the study of aggregate characteristics is considered very necessary in using SCC, many researchers have examined coarse aggregate properties and their effect on SCC properties in the fresh and hardened states.
Tviksta (2000) stated that it is possible to use natural, rounded, semi-crushed or crushed aggregates to produce SCC. The aggregates' characteristics should be taken into consideration for the performance required for fresh and hardened concrete (Neuwald, 2004 and Janssen, and Kuosa, 2001). The shape and size of coarse aggregate has a vital influence on the necessary mortar and paste volume to cover all particles. Naturally uncrushed gravel often needs less mortar or paste than does limestone. Granite, on the other hand, requires more mortar volume. Crushed aggregate tends to reduce flow because of the interlocking of the angular particles, whilst rounded aggregate improves the flow because of lower internal friction (Alexander and Prosk 2003). The key to successfully producing economical SCC, it should be observed, is to use a well-graded aggregate source. SCC mixes can use a poorly graded aggregate but this requires providing more viscosity to avoid segregation problems (Neuwald 2004). A high maximum size leads to decreased passing ability. Hence, decreasing the coarse aggregate content will be required. The choice of maximum size depends on the amount of reinforcement bars and the gaps between them, where higher proportions of higher maximum size may lead to aggregate blocking in the congested area with reinforcement bars. The optimum coarse aggregate content depends on two parameters. The first parameter is the maximum size, where lower values of maximum size lead to increased possibility of using high coarse aggregate content. The second parameter is the shape of the coarse aggregate, whether it's crushed or rounded, where a higher content of rounded shape leads to increased possibility of using a high coarse aggregate content (EFNARC 2002). While Petersson (1997) considered that the maximum size of aggregate (10mm and 20mm) that is suitable to produce SCC.
The objectives of the present study of the SCC System were to study the effect of three types of aggregate (crushed gravel, uncrushed gravel and crushed limestone), the maximum size (10 and 20), and the texture of the aggregate. Firstly, it was done by making a comparison among three types of local aggregate and their influence on the fresh and hardened properties of SCC. Secondly, the effect of sizes 10 and 20mm on the properties of SCC also were studied. Both the uncrushed and crushed aggregate were used to study the effect of texture surface of aggregate on the properties of SCC.
2 EXPERIMENTAL WORK MATERIALS
The cement used was ordinary Portland cement Type (I) (C), metakaolin (MK) was used as a partial replacement for cement with the percentage of replacement at (10%), and the fineness of MK being (17000) cm2/gm. Table (1) shows the chemical properties of this cement and metakaolin. Natural sand (S) was used (fineness modulus was 2.41, specific gravity: 2.62, absorption 0.83%, loose bulk density: 1730 kg/m3). In this study the three types of coarse aggregate (CA)were uncrushed gravel, crushed gravel, and crushed limestone with a maximum size of 20 mm and specific gravity (2.68, 2.62 and 2.58) and absorption (0.6,0.64 and 2%), respectively. And the range of Grading of theses types of aggregate in the
range of grading of BS 828-1992. The superplasticizer (SP) that was used was Glenium 51. Glenium 51 is considered one of the new generations of copolymer - based superplasticizers. ASTM C494-Type F designed for the production of SCC was used in this study. Glenium 51 has a light brown, a relative density of 1.1 @ 20 Co and a viscosity of 128 + 30 CPS @ 20 oC.
Table 1: Chemical properties of cement and MK
Chemical composition SiO2 AI2O3 Fe2O3 Na2O K2O CaO MgO SO3 L.O.I.
Cement 21.00 5.26 3.00 - - 62.00 2.70 2.10 1.10
Metakaolin 51.98 38.33 1.77 0. 38 0. 37 0. 36 0.13 0.12 6.56
3 EXPERIMENTAL PROGRAM
In order to achieve the aim of the study, the work was divided into 12 mixes and all details are shown in Table (2). These mixes were designed, mixed, tested for fresh properties and cast.
4 MEASUREMENTS AND PROCEDURE
The mix design method used in the present study is according to (EFNARC 2002) . The mix design has limited material proportion used in this study. The proportions of materials are (1:1.73:1.77) by weight. Where, the coarse aggregate content is 0.34 of the total volume of concrete. After determining the suitable mixture proportioning method and the materials for this study, no changes were made to all materials except the dosage of super-plasticizer and w/c to maintain the required workability.
5 TEST METHODS FOR SCC
In the fresh state, the tests are slump flow, V-funnel, L-box and U-box are all test methods used for the assessment of the fresh properties of SCC in this study. While compressive and flexural strengths and static modulus of elasticity are tests used for studying hardened properties.
6 RESULTS AND DISCUSSION
6.1 Fresh Properties
The fresh properties of each mix were evaluated and compared with previous work. The tests were carried out to determine the effect of maximum size, and type of coarse aggregate on the filling ability, passing ability and segregation resistance of SCC.
The flowing ability of fresh concrete is described by slump flow investigated with Abrams flow. Figure (1) shows the results of the slump flow tests. The values of T50cm represent the time required for the concrete flow to reach a circle with a 50cm diameter, while the values of (D) represent the maximum spread (slump flow final diameter). It is very clear from the results that all the mixes satisfy the requirements of SCC. Thus, all the mixes are assumed to have good consistency and workability from the filling ability point of view. However, these results show a wide range of variation. This variation illustrates the effect of coarse aggregate variables on the filling ability of SCC mixes. D was fixed at 700mm.
Table 2: Description of Mixes
Mix No. C (kg/m3) MK (kg/m3) W (kg/m3) SP (% of cement weight) S (kg/m3) CA (kg/m3) CA type CA max. size
CU10 500 0 170 0.85 865 885 Uncrushed 10
CU20 500 0 170 0.80 865 885 Uncrushed 20
C10 500 0 172 0.95 865 885 Crushed 10
C20 500 0 172 0.90 865 885 Crushed 20
CL10 500 0 172 1.00 865 885 limestone 10
CL20 500 0 172 0.95 865 885 limestone 20
MU10 450 0 175 1.70 865 885 Uncrushed 10
MU20 450 0 175 1.65 865 885 Uncrushed 20
MC10 450 0 175 1.85 865 885 Crushed 10
MC20 450 0 175 1.80 865 885 Crushed 20
ML10 450 0 173 1.80 865 885 limestone 10
ML20 450 0 173 1.75 865 885 limestone 20
Note: W is water that used in the mixes.
Fig. (1) indicates that the T50cm of mixes with (10mm) maximum size of coarse aggregate was less than the T50cm of mixes with (20mm) maximum size of coarse aggregate. This agrees with the study carried out by (Raheem 2005). Also the mixes made from uncrushed gravel had lower values of T50cm than the T50cm values of the mixes made from crushed gravel and crushed limestone, due to the smooth texture of the surface of uncrushed gravel.
Figure (1) shows that the incorporation of high reactivity metakaolin as a partial replacement by weight of cement leads to an increase in T50cm values. This is attributed to the fact that the high reactivity metakaolin has plate-like particles (Justice 2005) which increase the inter-particles friction (Hadhrati 2006).
d 5 0)
o £ 3
CU10 CU20 C10 C20 CL10 CL20 MU10 MU20 MC10 MC20 ML10 ML20 Mixes
Figure 1: Time required passing (50 cm Dia.) Circle (T50).
The values of the V-funnel test (flow time (Tf)) represent the ability of the concrete to flow out of the funnel), while the (Tf5min) values represent the same ability, but after refilling the funnel and allowing concrete to discharge after 5 minutes from the refilling. Figure (2) illustrates the results of the V-funnel test. No blocking or segregation is observed for all the mixes. The results clearly show the effect of maximum size and type of coarse aggregate on the ability of concrete to flow.
Figure (2) reveal the influence of the maximum size of coarse aggregate on Tf and Tf5min values. It can be seen from the figure that the larger maximum size of coarse aggregate leads to an increase in the values of and Tf5min.
From the test results presented in Figure (2), it is noticed that the mixes made from uncrushed gravel have values of and Tf5min less than the mixes made from crushed gravel and crushed limestone. The results shown in Figure (2) indicate that the incorporation of high reactivity metakaolin as a partial replacement by weight of cement give values of and Tf5min higher than mixes without high reactivity metakaolin. The results obtained show that the V-funnel test is more sensitive to the change in the properties of the concrete mixes than is the slump flow test.
Figure 2: Tf and Tf5 min (sec.) for all mixes.
1.2 n 1
p 0.8 -x t 0.6 cn
m 0.4 0.2
CU10 CU20 C10 C20 CL10 CL20 MU10 MU20 MC10 MC20 ML10 ML20
Figure 3: Results of BR for all mixes
The L-box and U-box are used to measure the filling ability and the passing ability of SCC mixes. The values of (H2/H1) represent the blocking ratio (BR), while the values of T20 to T40 represent the times of the concrete to reach 20 and 40 cm flow, respectively. The L-box test results are showed in Figure 3.
The values of (BR) and (T20, T40) are plotted in Fig. (3) and Fig. (4), respectively. Fig. (3, and 4) shows that the mixes with (20mm) maximum size of coarse aggregate give values of (BR) lower and higher values of (T20 and T40) as compared with mixes with the (10mm) maximum size of coarse aggregate. This is due to the tendency of the mixes with larger maximum size of coarse aggregate to jam
flowing, while the mixes with the smaller maximum size of coarse aggregate will flow freely without stopping.
It can be seen from Fig. (3) that, the mixes made from uncrushed gravel have better flow near the obstacles than the mixes made from crushed gravel and crushed limestone. This deformability depends on the size and grading of the coarse aggregate. As well as, (T20 and T40) values of mixes that have uncrushed gravel are less than that of the mixes that contain crushed gravel and crushed limestone. This is attributed to the smooth texture of the surface of uncrushed gravel that facilitates passing aggregate through obstacles.
Fig. (3) demonstrates that the incorporation of metakaolin as a partial replacement by weight of cement leads to an increase in T20cm and T40cm. as compared with mixes without metakaolin. This is due to the fineness of metakaolin that leads to increased viscosity of mixes.
Figure 4: Results of T20cm and T40cm for all mixes.
This test is used to measure the filling ability of SCC. In this test, the degree of comparability can be indicated by the height that the concrete reaches after passing through obstacles. The values of filling height (AH=h1-h2) represent the ability of the concrete to fill the second compartment when the sliding gate is opened. Test results are showed in Figure (5) which indicates that the ranges of results are between (0-30) mm. All mixes showed excellent deformability without segregation.
35 30 — 25
CM ■C
^ 20 .c
i 15 = 10 5 0
CU10 CU20 C10 C20 CL10 CL20 MU10 MU20 MC10 MC20 ML10 ML20
Figure 5: Results of U-box test (AH) cm.
6.2 Mechanical Properties of SCC
From the test results presented in Figures (6,7, and 8), it can be noticed that the compressive and flexural strength and modulus of elasticity of the mixes made with the 10mm maximum size of coarse aggregate is higher than the values of the mixes made with the 20mm maximum size of coarse aggregate. This is due to the smaller maximum size of coarse aggregate that has the larger surface area that results in a higher bonding strength in the transition zone (ITZ) around aggregate particles when concrete is under loading. This is in agreement with (Aulia, and Deutschmann. 1999).
The effect of the coarse aggregate type on compressive strength is shown in Fig. (6, 7), where the results show that crushed limestone in the mixes gave higher compressive and flexural strengths and modulus of elasticity than crushed gravel in the mixes. This behavior is attributed to the effect of chemical interaction and the rougher surface texture of particles, where the bond between aggregate and paste is stronger. In addition, the results indicate that mixes that have crushed gravel give (compressive and flexural) strength and modulus of elasticity values higher than uncrushed gravel. This may be attributed to the roughness of the surface of crushed gravel as compared with the surface of uncrushed gravel. This agrees with (Druta 2003)
SE 100
a F 20
CU10 CU20 C10 C20 CL10 CL20 MU10 MU20 MC10 MC20 ML10 ML20
□ 7-day ■ 28-day
□ 56-day
□ 90-day
Figure 6: Results of Compressive strength (fcu) of all mixes.
Figure 7: Results of flexural strength (fr) of all mixes SCC.
Figure 8: Modulus of Elasticity (Ec) for all Mixes SCC.
Fig. (6) shows the effect of the incorporation of metakaolin as a partial replacement by weight of cement. The results show that the compressive strength values of mixes with metakaolin at age of 7 days were lower by about (-7.5 to -12%) than those without metakaolin. This is due to the dilation effect of metakaolin, when it is used as a partial replacement for cement. The concrete mixtures will also experience some effect of the removal of cement from the reacting system and that affecting the early compressive strength of concrete. This agrees with (al-Jabri 2005). However, at 28, 56 and 90 days, the compressive strength of mixes was higher than in those without metakaolin. This behavior was due to the pozzolanic activity of metakaolin on hydration of cement, where metakaolin reacted with Ca (OH)2 and this reaction led to augmentation in the densification of the transition zone and thus increased the bonding strength at the interface zone and the formation of microcracking was decreased. Hence, the microcracking initiation occurred at a higher stress level (Aulia and Deutschmann 1999).
7 CONCLUSIONS
The following conclusions can be drawn, based on the results of this work:
1. The flowability of SCC decreases with the increase in the maximum size of coarse aggregate and using crushed aggragate with the same W/P ratio and superplasticizer dosage.
2. The employment of 10% metakaolin as a partial replacement by weight of cement leads to a decrease in flowability and an increase in viscosity and improving the strength at (28, 56, 90) days of testing.
3. Concrete mixes made with crushed limestone give higher strength and elasticity than concrete mixes made with crushed gravel, and concrete mixes made with crushed gravel gave higher strength and elasticity than concrete mixes made with uncrushed gravel.
4. The mechanical properties of SCC mixes containing the 10 mm maximum size of coarse aggregate are higher than in mixes with the 20 mm maximum size of coarse aggregate.
References
[1] Ahmed, S. (1994), ''high performance concrete'' A State-of-Art Report, pp.1-9.
[2] Alexander, C. and Prosk (2003), T.,'' Self-Compacting Concrete-Influence of the Coarse Aggregate on The fresh Concrete Properties" http://www.darmstadt-concrete.de , , pp. 1-4.
[3] Al-Jabri, L.A. 2005," The Influences of Mineral Admixtures and Steel Fibers on the Fresh and Hardened Properties of SCC", M.Sc. Thesis, Al-Mustansiriya University, pp.135.
[4] Aulia T.B. and Deutschmann K (1999)., "Effect of Mechancal Properties of Aggregate on the Ductility of High Performance Concrete ", Leipzig University, LACER No.4,.
[5] Druta, C 2003., "Tensile Strength and Bonding Characteristics of Self-Compacting Concrete", M.Sc. Thesis, Louisiana State University, , 125 pp.
[6] EFNARC 2002,, "Specification and Guidelines for Self-Compacting Concrete", pp.32, www.efnarce.org.
[7] Hadhrati, H., F. 2006, "Mechanical Properties of Self-Compacting High Performance Structural Lightweight Aggregate Concrete" MSc. Thesis, University of Technology, pp.60-65.
[8] Hwang, S., Kayat, K., and Banneau, O. 2006, "Performance-Based Specifications of Self-Consolidating Concrete Used in Structural Applications" ACI Material Journal, Title no.103-m14, pp.122.
[9] Janssen, D., and Kuosa, H 2001., '' Self-Compacting Concrete: Theory to Practice'', Report No.4, pp.21-24.
[10] Justice, J.M. 2005, "Evaluation of Metakaolin for Use as Supplementary Cementitious Materials", M.Sc. Thesis, Georgia Institute of Technology, pp.134
[11] M.Collepardi 2001, "A very Close Precursor of Self-compacting Concrete ", Symbosium on Sustainable Development and Concrete Technology, Proceeding of the Giornate AICAP, Ravenna (Italy),.
[12] Martys, N., and Ferraris, C. 2003, "Simulation of SCC Flow", Building and Fire Research Laboratory National Institute of Standard, Chicago,, , pp. 27-30.
[13] Neuwald, A (2004)., '' Self-Consolidating Concrete" MC Magazine, pp. 2-4.
[14] Ozawa k., Okamura, H. and Maekawa 1992, K. "Development of High Performance Concrete'' University of Tokyo, Factulty of Engineering Journal, , 156 pp.
[15] Petersson, O. (1997), "Preliminary Mix Design''Final Report of Task 1, Sweedish Cement and Concrete Research Institute, pp.15-19.
[16] Raheem, J., O 2005., '' The Influence of Volume Ratio and Size of Coarse Aggregate on the Properties of Self-compacting Concrete'' MSc. Thesis, Department of Civil Engineering, College of Engineering, Al-Mustansiriya University, (December).
[17] Tviksta L.G (2000)., "Guideline for SCC ", Brite EuRam, Task 9 End Product, pp.3-11.
