Indian Journal of Engineering & Materials Sciences Vol. 13, June 2006, pp. 247-252
Effects of expanded perlite aggregate and different curing conditions on the drying shrinkage of self-compacting concrete İbrahim Türkmen* & Abdulhamit Kantarci Department of Civil Engineering, Atatürk University 25240, Erzurum, Turkey Received 26 April 2005; accepted 3 March 2006 Fresh self-compacting concrete (SCC) flows into place and around obstructions under its own weight to fill the formwork completely and self-compact, without any segregation. The present study investigates drying shrinkage of SCC including mixtures of expanded perlite (EPA) and natural aggregates (NA) at six different curing conditions. The binder dosage is kept constant at 450 kg/m3 throughout the study. A superplasticizer is used as 2% (by weight) of Portland cement (PC) to reduce water/cement+mineral (w/cm) ratios and self-compacting. Specimens have been exposed to conditions of lime-saturated water (B1), dry in air (B2), coated with paraffin (B3), three times wetted in a day (B4), under wet-sack (B5) and 100% relative humidity (B6). It has been found that drying shrinkage of concrete is reduced by using EPA. The drying shrinkage of EPA concrete decreases with an increasing moisture content. It is also found that concrete exhibits a lower drying shrinkage in all time periods under the B1 curing conditions. IPC Code: E04G21/08
The use of self-compacting concretes (SCC) lowered the noise level on the construction site and diminished the effect on the environment1 and improved the quality of concrete in-situ2. SCC is a new category of high-performance concrete (HPC), characterized by its ability to spread into place under its own weight without the need of vibration, and self-compact without any segregation and blocking. The introduction of SCC represents a major technological advance, which leads to a better quality of concrete produced and a faster and more economical concrete construction process3. The use of SCC in civil engineering has gradually increased over the past few years, as reported earlier1-8. The workability of SCC is higher than the highest class of consistence described within EN 206 and can be characterized by the properties like; filling ability, passing ability and segregation resistance. A concrete mix can only be classified as SCC if the requirements for all three characteristics are fulfilled9. The most popular way of light-weight concrete (LWC) production is by using light-weight aggregate (LWA)10. LWC mixes are generally of low water/cement-mineral (w/cm) to compensate for the aggregate weakness. LWC have certain properties that are distinctly different from normal weight concrete (NWC). In addition to low unit weight, better reinforcing steel-concrete bond, durability ______________ *For correspondence (E-mail:
[email protected])
performance, tensile strain capacity, and fatigue resistance make it preferable to NWC11. There are a number of methods to produce LWC. In one method, the fine portion of the total concrete aggregate is omitted, which is called ‘no-fines’. Another way of producing LWC is to introduce stable air bubbles inside concrete by using chemical admixtures and mechanical foaming. This type of concrete is known as aerated, cellular or gas concrete. The most popular way of LWC production is use light-weight aggregate12. In recent years, LWC with high strength or high workability have been widely developed13. A number of studies14-17 have been conducted on the shrinkage of concrete made with light-weight aggregate concretes and mineral admixture cements. Kohno et al.14, reported that the autogenous shrinkage of concrete is reduced by using light-weight aggregate (LW) and that the autogenous shrinkage of LW concrete decreases with an increasing moisture content. Pietro et al.15, indicated that, at the temperatures tested, concrete made with blast furnace slag cement shows higher shrinkage in the first days than concrete made with Portland cement (PC). Collins and Sanjayan16, reported that the capillary tensile forces set up during drying is an important contributory factor for the drying shrinkage of concrete. Kayali et al.17, reported that shrinkage of normal weight concrete stabilized after 400 days, while shrinkage of LW concrete did not appear to stabilize after a similar period of continuous drying.
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These light-weight aggregates have created a considerable interest in recent years, because their application may improve properties such as the workability, strength, and resistance to freezing and thawing of LWC. Most of the experimental research on shrinkage has been concentrated on natural aggregate mixtures. In this study, the influence of expanded perlite aggregate (EPA), curing time and curing conditions on the drying shrinkage of SCC has been investigated. Materials and Methods Materials
ASTM Type I PC, SP (Superplasticizer-ViscoCrete 3075), SF and EPA were provided from Erzurum Aşkale Cement, Sika Company, Istanbul, Antalya Electro Metallurgy Enterprise and Etibank Perlite Expansion Enterprise, Izmir, Turkey, respectively. The chemical compositions of the materials used in this study are summarized in Table 1. The physical and mechanical properties of the PC used are given in Table 2. A SP based on chains of modified polycarboxylic ether was used as a SP, compatible with ASTM C 494 F at a dosage of 2% of cement. Table 1—Chemical analysis of PC, SF, EPA (%) Component SiO2 Fe2O3 Al2O3 CaO MgO SO3 K2O TiO2 Na2O Sulphide (S-2) Chloride (Cl-) Undetermined Free CaO LOI
PC (%)
SF (%)
EPA (%)
20.06 3.6 5.16 62.43 2.82 2.32 0.6 0.2 0.36 0.17 0.04 1.05 0.71 1.55
93.7 0.35 0.3 0.8 0.85 0.34 0.1-0.3 0.5-1.0
71-75 12-16 0.2-0.5 2.9-4 -
Table 2—Physical and mechanical properties of PC Specific gravity (g/cm3) Specific surface (cm2/g) Remainder on 200-micron sieve (%) Remainder on 90-micron sieve (%) Volume expansion (Le Chatelier, mm) 2 days Compressive strength 7 days (MPa) 28 days
3.15 3410 0.1 3.1 24.5 42.0 44.4
Coarse aggregate consisted of crushed basalt. The specific gravity, maximum size and absorption of this aggregate were 2.64, 16 mm and 2%, respectively. Sand was used as a fine aggregate having a specific gravity and absorption of 2.31 and 4%, respectively. The mix proportions of these mixes are given in Table 3. The binder (PC+SF) content was 450 kg/m3 of concrete. Four main groups of mixes of natural aggregate (NA) and EPA were produced. They were specified as EPA0 (100%NA), EPA5 (95%NA+5%EPA), EPA10 (90%NA+10%EPA), EPA15 (85%NA+15%EPA). For all groups PC-SF mixtures were prepared adding 10%SF in replacement of PC. The counter mixes were prepared in a laboratory countercurrent mixer for a total of 5 min. Water/cement+mineral (w/cm) ratio was kept constant at 0.35. Fig. 1 shows 28-dry unit weight of SCC specimens according to different EPA ratios. Six types of curing conditions as shown in Figs 2-7 were chosen to study the effect of curing environment on the performance EPA concrete and control concrete. Figs 2-11 shows the results obtained up to 150 days. Concrete specimens, 7×7×28 mm, were stored in these six curing environments until tested. The exposure of specimens was carried out for 3, 7, 14, 28, 56, 90, 120 and 150 days. For each mix, three specimens’ 100×200 mm cylinders and 70×70×280 mm were prepared. After 1 day of wet curing, the specimens were stored at constant temperature in lime-saturated water (B1), dry in air (B2), coated with paraffin (B3), three times wetted day for 14-days Table 3—Mix proportions of all groups Mixtures w/cm Water, kg/m3 Cement, kg/m3 Silica Fume kg/m3 Sand 0-4 mm EPA, 0-4 mm Gravel 4-8 mm Basalt 8-16 mm Superplasticizer, kg/m3 Density, Slump flow (cm) L-box (H2/H1) V-funnel (sec) J-ring (mm)
Aggregates Sizes (kg/m3)
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EPA(%) 0
5
10
15
0.35 170.8 405 45 598
0.35 174.37 405 45 523
0.35 178 405 45 448
0.35 181.59 405 45 374
-
5.27
10.54
15.82
428
428
428
428
604
604
604
604
9
9
9
9
2260 61 0.9 9 7
2193 58 0.8 11 9
2128 59 0.8 10 8
2063 59 0.8 10 7
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Fig. 1— 28-Dry unit weight of concrete specimens according to EPA ratio
Fig. 2— Effects of % of EPA and age on the drying shrinkage of specimens in the B1 condition
Fig. 3— Effects of % of EPA and age on the drying shrinkage of specimens in the B2 condition
Fig. 4— Effects of % of EPA and age on the drying shrinkage of specimens in the B3 condition
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Fig. 5— Effects of % of EPA and age on the drying shrinkage of specimens in the B4 condition
Fig. 6— Effects of % of EPA and age on the drying shrinkage of specimens in the B5 condition
Fig. 7— Effects of % of EPA and age on the drying shrinkage of specimens in the B6 condition
Fig. 8— Effects of curing conditions and age on the drying shrinkage of EPA0
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Fig. 9— Effects of curing conditions and age on the drying shrinkage of EPA5
Fig. 10— Effects of curing conditions and age on the drying shrinkage of EPA10
Fig. 11— Effects of curing conditions and age on the drying shrinkage of EPA15
(B4), under wet-sack for 14-days (B5) and 100% constant relative humidity (B6) while measuring drying shrinkage at different curing times. B3 curing is considered to minimize the moisture loss from the surface of concrete. Methods Workability tests
Several methods exist to evaluate the workability of fresh SCC2,18, such as standard slump and slump flow, L-box test, J-ring, V-funnel, Orimet method,
segregation resistance (stability) and passing ability (resistance to blocking). Fresh SCC tests were made in accordance with EFNARC specification9. The workability properties of the fresh concrete other than slump were evaluated, since in this case the slump value is not relevant the concrete being very fluid. Therefore, the attention was focused on the measurement of the slump flow. To characterize the consistency of the prepared concrete, a workability test (slump flow test) was performed on site. This was in the form of a slump test using the Abrams cone method. However, the average diameter of the spread concrete is measured a minute later. The L-box test assesses the flow of the concrete, and also the extent to which it is subject to blocking by reinforcement. The apparatus consists of a rectangular-section box in the shape of an ‘L’, with a vertical and horizontal section, separated by a moveable gate, in front of which vertical lengths of reinforcement bar are fitted. The vertical section is filled with concrete, and then the gate lifted to let the concrete flow into the horizontal section. When the flow has stopped, the height of the concrete at the end of the horizontal section, H2, is expressed as a proportion of that remaining in the vertical section, H1. This is an indication passing ability, or the degree to which the passage of concrete through the bars is restricted. The described V-funnel test is used to determine the filling ability (flowability) of the concrete with a maximum aggregate size of 20 mm. The funnel is filled with about 12 L of concrete and the time taken for it to flow through the apparatus is measured. The J-ring test is used to determine the passing ability of the concrete. The equipment consists of a rectangular section (30 mm×25 mm) open steel ring, drilled different diameters and spaced at different intervals: in accordance with normal reinforcement considerations, 3x the maximum aggregate size might be appropriate. The diameter of the ring of vertical bars is 300 mm, and the height 100 mm. Hardened concrete
Prismatic specimens for drying shrinkage were prepared according to ASTM C 157-93. This test method covers the determination of the length changes of hardened hydraulic-cement mortar and concrete due to causes other than externally applied forces and temperature changes. This test method is particularly useful for comparative evaluation of this potential in different concrete mixtures.
TÜRKMEN & KANTARCI: SELF-COMPACTING CONCRETE
Results and Discussion Workability
Slump flow is correlative with viscosity. The results indicate that the viscosity of fresh concrete is too low to resist segregation. A spread of 59 cm was averagely seen for this concrete. Djelal20 reported the similar results for slump flow. The L-box tests shown that there is a serious lack of stability of segregation (see Table 3). If the concrete flows as freely as water, at rest it will be horizontal, so H2/H1=1. Therefore the nearer this test value, the blocking ratio, is to unity, the better the flow of the concrete. The EFNARC specification9 suggested a minimum acceptable value of 0.8. In this study, blocking ratios were obtained between 0.8 and 0.9. Therefore, these values can be acceptable for blocking ratio of SCC in accordance with EFNARC9. As it can be seen in Table 3, Vfunnel time was achieved between 9 and 11 s. These values can be acceptable for filling ability of SCC in accordance with EFNARC9. The measure of difference in height between the concrete just inside the bars and that just outside the bars for J-ring test can be seen in Table 3. It was calculated that the average of the difference in height at four locations (in mm). In the result of the J-ring tests was obtained values between 7 and 9 mm, which are convenient to those reported between 0 and 10 mm for J-ring test by EFNARC 9. Dry unit weight
The results of 28-days’ dry unit weight are shown in Fig. 1. According to the obtained data, it was observed that unit weights of 28-day hardened concrete decreased with increasing EPA in the mixtures, because the specific gravity of EPA is lower than that of NA. The highest unit weight was 2345 kg/m3 at 100%NA samples. The lowest unit weight was 2300 kg/m3 at 85%NA+15%EPA samples. Effects of EPA on drying shrinkage
The results of the 3, 7, 14, 28, 56, 90, 120 and 150 days drying shrinkage according to EPA ratio and curing time were given in Figs 2-7. According to Fig. 2, using EPA replacement of NA 0%, 5%, 10%, 15% allows us to decrease the 3-150 days drying shrinkage of specimens in B1 condition. However, according to Fig. 3, using EPA replacement of NA 0%, 5%, 10%, 15% allows us to increase the 3-150 days drying shrinkage of specimens in the B2 condition. In all the other conditions, using EPA replacement of NA 0%, 5%, 10%, 15% allows us to
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decrease the 3-150 days drying shrinkage of specimens (see Figs 4-7). From Figs 2-7, it can be noted that the drying shrinkage of EPA concrete is generally smaller than that of NA concrete except in B2 condition. The important findings in this study are that the drying shrinkage of concrete is reduced by using EPA14, and the drying shrinkage depends on time, curing conditions, and unit quantity of EPA. At the early stage of hardening, most of the capillarity pores and most of the light-weight aggregate particles are fully saturated with water. As the hydration reaction progresses, the capillarity water are consumed to form new and fine capillarity pores. However, the internal relative humidity in the capillarity pores is not lowered due to a continuous supply of moisture from the EPA particles. As a result, the cement paste does not shrink. As Figs 2 and 4-7 show, the drying shrinkage of the EPA concrete is smaller than that of the NA concrete. The reduction of drying shrinkage of the EPA concrete may be due to the of immediate replacement moisture from the EPA to the cement paste. Effects of curing conditions on the drying shrinkage
The effects of six different curing conditions on the drying shrinkage of both EPA and NA concrete were determined on the 3, 7, 14, 28, 56, 90, 120 and 150 days and the results were given in Figs 8-11. The drying shrinkages of specimens were lowest in B1 until 150 day for EPA0. The drying shrinkages of specimens were highest in B2 until 150 day for EPA0, EPA5, EPA10 and EPA15 (see Figs 8-11). In short, drying shrinkage decreases with increasing moisture content of curing conditions. Drying shrinkage reached about 2068×10-6 in B2 condition after 150 days. However, the lowest drying shrinkage was observed at B1 condition because of saturated to water. From Figs 8-11, it can be noted that the drying shrinkages of B1, B3, B4, B5 and B6 conditions are generally smaller than that of B2 condition. The drying volume change of EPA concrete is directly related to the adsorption capacity of the aggregate and moisture content of condition14. Conclusions The following conclusions can be drawn from this study: The incorporated of EPA to the mixes up to 15%, it was achieved that a production of SCC according to test results which has sufficient properties of viscosity, filling ability, passing ability and blocking ratio. The dry unit weight of SCC with higher EPA
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contents decreases. The inclusion of EPA to the mix decreases the tendency of the mix to drying shrinkage except for B2 condition. The drying shrinkage of EPA concrete is smaller than that of normal concrete in moisture conditions and the drying shrinkage of EPA concrete is higher than that of normal concrete in dry conditions. The drying shrinkage of EPA concrete may be related directly to the adsorption capacity of the aggregate. With increasing of moisture content and unit quantity of EPA drying shrinkage of EPA concrete decreases. References 1 Persson B, Cem Concr Res, 31 (2001) 193-198. 2 Xie Y, Liu B, Yin J & Zhou S, Cem Concr Res, 32 (2002) 477-480. 3 Sonebi M, Cem Concr Res, 34 (2004) 1199-1208. 4 Sari M, Prat E & Labastire J-F, Cem Concr Res, 29 (1999) 813-818. 5 Persson B, Cem Concr Res, 33 (2003) 1933-1938. 6 Poon C S, & Ho D W S, Cem Concr Res, (in press). 7 Lachemi M, Hossain K M A, Lambros V, Nkinamubanzi P-C & Bouzoubaa N, Cem Concr Res, 34 (2004) 185-193.
8 Jooss M & Reinhardt Hans W, Cem Concr Res, 32 (2002) 1497-1504. 9 EFNARC, Specification and Guidelines for Self-Compacting Concrete, February, 2002 10 Bingöl A F & Gül R, Indian J Eng Mater Sci, 11 (2004) 6872 11 Gesoğlu M, Özturan T & Güneyisi E, Cem Concr Res, 34 (2004) 1121-1130. 12 Demirboğa R, Örüng İ & Gül R, Cem Concr Res, 31 (2001) 1627-1632. 13 Wasserman R & Bentur A, Cem Concr Compos, 18 (1996) 67-76. 14 Kohno K, Okamoto T, Isikawa Y, Sibata T & Mori H, Cem Concr Res, 29 (1999) 611-614. 15 Lura P, Breugel K V & Maruyama I, Cem Concr Res, 31 (2001) 1867-1872. 16 Collins F & Sanjayan J G, Cem Concr Res, 30 (2000) 14011406. 17 Kayali O, Hague M N & Zhu B, Cem Concr Res, 29 (1999) 1835-1840. 18 Okamura H, Concrt Int, 19 (7) (1997) 50-54. 19 Corinaldesi V & Moriconi G, Cem Concr Res, 34 (2004) 249-254. 20 Djelal C, Vanhove Y & Magnin A, Cem Concr Res, 34 (2004) 821-828.
