Influence of steam curing on hardened properties of recycled aggregate concrete

Abstract

The effects of steam curing on the hardened properties of recycled aggregate concrete were investigated. In this study, two series of concrete mixtures with water/cement ratios of 0 . 55 and 0 . 45 were prepared. Recycled aggregates were used as 0, 20, 50 and 100% by volume replacements of natural coarse aggregate in the concrete mixtures. The concrete specimens underwent standard water-curing and steam-curing regimes. The test results showed that the strength of concrete decreased as the recycled aggregate content increased. An initial steam-curing regime increased the one-day strength of the concrete, but the corresponding 28-and 90-day strengths decreased. Furthermore, steam curing reduced the static modulus of elasticity of concrete compared with that of the water cured concrete. However, the negative effect of steam curing diminished as the recycled aggregate content increased. Moreover, steam curing decreased the drying shrinkage and increased the resistance against chloride ion penetration of the recycled aggregate concrete. The results demonstrate that one of the practical ways to utilise a higher percentage of recycled aggregates in concrete is 'precasting' with an initial steam curing stage immediately after casting. IntroductionRecycled aggregate (RA) has been used as a replacement of the natural aggregate for a number of years. The potential benefits and drawbacks of recycled aggregate concrete, when compared with equivalent concrete using natural aggregate, have been quite extensively studied. 1-11 The use of recycled aggregate generally increases the drying shrinkage, creep, carbonation rate and water sorptivity and decreases the compressive strength, modulus of elasticity and resistance to freezing and thawing of concrete compared with those of natural aggregate concrete. Hasaba et al. 12 reported that the drying shrinkage of concrete prepared with coarse recycled aggregate and natural sand was 50% higher than that of conventional concrete. When both coarse and fine recycled aggregates were used, the drying shrinkage of recycled aggregate concrete was as much as 70% higher than that of conventional concrete. Hansen and Boegh 13 reported that recycled aggregate concrete had 15 to 30% lower modulus of elasticity and 40 to 60% higher shrinkage than those of conventional concrete. Olorunsogo and Padayachee 14 found that the water sorptivity of concrete prepared with 100% recycled aggregate (by weight replacement) was approximately 39% greater than that of natural aggregate concrete at the curing age of 28 days. Dhir et al. 15 showed that the reduction in compressive strength of water-cured RC 30 (characteristic strength of 30 MPa) concrete measured at one year was less than 6 MPa regardless of the coarse recycled aggregate content.The negative effects of recycled aggregate on concrete quality limit the use of this material in structural concrete. However, the disadvantages of using recycled aggregate can be minimised in the precast concrete industry since it is easier to ensure the quality of such ...

Recycled concrete with coarse recycled aggregate. An overview and analysis

“…Humidity and temperature are key factors on shrinkage development leading to higher drying shrinkage when humidity lessens, or greater shrinkage at high temperatures (85). Additionally, the curing process may reduce the concrete strain due to shrinkage (86,87). In a recent research, Hanif et al (88) reported that the use of recycled aggregates with high early strength cement and steam curing method led to an improvement of shrinkage performance, lowering early-age cracking.…”

Prediction of Chloride Ion Penetration of Recycled Aggregate Concrete

“…Kou et al 50 and Poon et al 57 studied the effect of applying a steam curing regime to specimens with increasing coarse RCA content. Steam-cured specimens showed an average of 20% and 30% less chloride ion penetration at 28 and 90 days, respectively, than mixes subjected to standard curing.…”

“…Furthermore, according to Piaw 119 , the coefficients of correlation (R) show that there is a very strong correlation between the two variables. A similar analysis ( Figure 6) was performed with the total charge passed of RAC mixes produced with binder equivalent to CEM I 27 , based on 123 measurements sourced from 16 publications 44,46,[50][51][52][53][54]57,59,60,[75][76][77]81,82,87 . As in Figure 4, factors related to the use of RA in concrete, known to have a significant influence on the resistance to chloride ion penetration, appear to have had marginal effect on the relationship between the total charge passed and compressive strength.…”

Influence of different types of fiber on the properties of recycled aggregate concrete

“…Consequently the mechanical and durability properties of recycled aggregate concrete are considerably lower than the normal concrete particularly at 100% recycled coarse aggregate. At 100% recycled coarse aggregate, the compressive strength of RAC is lowered by 17–30%; 15–45% lower by modulus of elasticity; 7–26% by split tensile strength, and 5–29% by flexural strength . The variation in the results of RAC is mainly attributed to the adherence of quality and quantity of old mortar to the recycled coarse aggregate.…”