# Coefficient of Thermal Expansion of RCA Concrete Made by Equivalent Mortar Volume
###### Abstract  
The present study was conducted to experimentally verify if the coefficient of thermal expansion (COTE) of recycled aggregate concrete is proportional to the volume of the original virgin aggregate in the total recycled aggregate concrete mix. Three types of recycled concrete aggregate (RCA) were crushed from: railroad concrete sleepers; precast (PC) culverts; commercial recycling plant. RCA concretes were mixed using two concrete mixing methods: conventional mix method and equivalent mortar volume (EMV) method. And by varying the replacement ratio, three test series were made. Test results showed that at the same RCA replacement ratio of 68%, the COTE of RCA concrete prepared by the EMV mix design was over 6-7% lower than that of RCA concrete made with the conventional mix method. It was also similar to or 1-2% lower than that of the natural coarse aggregate concrete. This may be because the conventional mix method does not take into account the residual mortar content attached to RCA. This results in a decrease in the volumetric ratio of the original virgin aggregate and a relative increase in the volumetric ratio of the mortar (or cement paste). recycled concrete; aggregate; mix proportioning; thermal expansion; mortar  
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concrete pavement have ended in failure, because, although not clarified yet, the COTE of RCA concrete is larger than that of conventional concrete prepared by mixing natural coarse aggregate, possibly making the concrete pavement vulnerable to blow-up. In other aspects, global warming problems led some researchers to consider sustainability including environmental benefits and innovative new materials and construction methods incorporating various other eco-friendly supplementary cementitious materials [7; 8; 9]. Heat energy was harvested from geothermal pavement constructed with construction and demolition waste materials [7]. The solar radiation can be absorbed by placing pipes in the pavement systems and circulating water in the pipes to collect the heat energy, to maximize the sustainability and energy efficiency of the infrastructures [7]. Feasibility of using demolished concrete block (DCB) was explored in a continued effort of material recycling [8]. The DCBs were used with self-compacting concrete (SCC) to produce DCB-filled-concrete since SCC can easily fill up the voids between DCBs. In addition to the traditional material testing properties such as mechanical strength and durability properties, the importance of the sustainability indicator which is a function of strength, resilience, ecology and economy has been emphasized [9]. The COTE of concrete is dependent on the concrete mixes [10; 11; 12; 13], ages [10; 11; 12; 13; 14; 15], humidity conditions [10; 11; 12; 13; 16; 17], temperature cycles [18; 19; 20] and types of aggregate [10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22; 23; 24; 25; 26; 27; 28; 29; 30; 31; 32; 33; 34; 35; 36; 37; 38; 39]. Since the COTE of cement paste is generally higher than that of aggregate, the COTE of concrete may differ according to the volumetric ratio of the aggregate in the mix [10; 11; 12; 13]. A large difference of the COTE between cement paste and aggregate has a significant impact on concrete durability [13]. [PERSON] [12] reported, based on data provided by [PERSON] [14] and [PERSON] and [PERSON] [15], that the COTE shows a noticeable increase in the early material ages, but gradually decreases with an increase in age. It is generally known that the COTE of moist cured specimens is higher than that of air-dried specimens [16]. However, [PERSON] [17] more systematically reported variations of the COTE according to the relative humidity; the results are accepted as generalizations in well-known textbooks on concrete, such as [PERSON] [10] and [PERSON] [11].