The cause and influence of self-cementing properties of fine recycled concrete aggregates on the properties of unbound sub-base.
The use of coarse recycled concrete aggregates (CRCA) in conjunction with fine recycled concrete aggregates (FRCA) as sub-base materials has been widely studied. Although research results indicate that it is feasible to employ both CRCA and FRCA as granular sub-base, the influence of the unhydrated cement in the adhered mortar of the RCA on the properties of the sub-base materials has not been thoroughly studied. Generally, it is known that the strength of the sub-base materials prepared with RCA increases over time. However, this mechanism, known as the self-cementing properties, is not well understood and is believed to be governed by the properties of the fine portion of the RCA (<5mm). This paper presents an investigation on the cause of the self-cementing properties by measuring X-ray diffraction patterns, pH values, compressive strength and permeability of various size fractions of the FRCA obtained from a commercially operated construction and demolition waste recycling plant. Their influence on the overall sub-base materials was determined. The results indicate that the size fractions of <0.15 and 0.3-0.6mm (active fractions) were most likely to be the principal cause of the self-cementing properties of the FRCA. However, the effects on the properties of the overall RCA sub-base materials were minimal if the total quantity of the active fractions was limited to a threshold by weight of the total fine aggregate.
Poon
Chi-Sun
CS
Department of Civil and Structural Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong. cecspoon@polyu.edu.hk <cecspoon@polyu.edu.hk>
Qiao
X C
XC
Chan
Dixon
D
D003252:Construction Materials / Q000032:analysis*; D006723:Hong Kong; D006863:Hydrogen-Ion Concentration; D008422:Materials Testing; D010316:Particle Size; D012037:Refuse Disposal / Q000379:methods*; D014961:X-Ray Diffraction