[A-GE28] Energy-Environment-Water Nexus and Sustainable Development

[AGE28-05] Measurements of CBR and particle breakage of recycled concrete aggregates blended with AAC grains for unbound road base materials in Vietnam

*Van Nam Pham¹, Van Doan Nguyen¹, Akihiro Matsuno¹, Kengo Nakamura¹, Hoang Giang Nguyen², Ken Kawamoto^1,2 (1.Graduate School of Science and Engineering, Saitama University, 255 Shimo-okubo, Sakura-ku, Saitama City, Saitama Prefecture 338-8570, Japan, 2.Hanoi University of Civil Engineering, 55 Giai Phong, Hai Ba Trung, Hanoi, Vietnam)

Keywords:California bearing ratio, Compaction, Particle breakage, Recycled concrete aggregates, Autoclaved aerated concrete

Permeable pavement system is normally designed to reduce surface runoff and to promote internal drainage and infiltration. Nowaday, it is also required not only to control the water permeasility but also to enhance water retention in the unbound road base layer made from recycled concrete aggregate (RCA). One of effective approaches to improve the water retention capacity is mixing/blending a high water absorbing porous material such as autoclaved aerated concrete (AAC) grains with RCA. But, the mixing/blending of AAC grains may reduce the mechanical strength of road base layer due to the particle breakage. This study, therefore, investigated the mechanical properties such as compaction and bearing capacity for the RCA samples blended with AAC grains. The tested RCA and AAC were made from construction and demolision waste and scrap in Vietnam. First, poor-graded RCA with a maximum diameter of 37.5 mm blended with AAC grains with % of substitution (f_s) on the mass basis varied from 0 to 50% (RCA100%, RCA95%+AAC5%, RCA90%+AAC10%, RCA70%+AAC30%, and RCA50%+AAC50%) were prepared, and laboratory tests to measure compaction curves and bearing capacity (California bearing ratio; CBR) were carried out. Besides, the particle breakage for tested samples were characterized comparing the particle size distributions before and after compaction process and the overall particle breakage (B_g) and the % increment and/or decrement in each fraction were determined. The results showed that the CBR values of the tested sample linearly decreased with increasing of f_s and dry density for samples of 0 to 50%, and with a smaller degree thereafter. The existence of coarse aggregates of AAC grains (i.e., 4.75 - 9.5 mm) which played as a framework might lead to a lesser degree of samples with % of AAC ≧ 50%. This might indicate that the framework would be dominated by AAC grains if the mixing proportion exceeded 50% and/or if coarse aggregates (i.e., ≧ 4.75 mm) were used. The % decrement of the coarse fraction of 25 - 37.5 mm and/ or 19 - 25 mm decreased with increasing up to 30% of AAC mixing proportion might be due to the cushioning effect of AAC grains, but cannot maintain the high CBR as compared to the sample of RCA100%. Among the granulometric properties, the B_g, dry density, and f_s, the CBR is largely controlled by dry density and f_s. The decrease in CBR with increasing B_g for samples of high f_s (i.e., ≧ 30%) was also observed.