# Coefficient of Thermal Expansion of RCA Concrete Made by Equivalent Mortar Volume
###### Abstract
In detail, the COTE of concrete is small at a relative humidity of about 20% but drastically increases at a relative humidity of 60-70%, showing its smallest value at a relative humidity of 100% [17]. Based on these results, the AASHTO TP 60 [18] provides a method for estimating the COTE while immersing a concrete specimen in a water bath. [PERSON] [19] showed that the COTE is dependent on the temperature cycle. The COTE during a temperature rise is different from that during a temperature drop, and the difference is introduced as the effect of thermal creep. Considering this, the AASHTO TP 60 [18] stipulates that a temperature cycle including an interval of temperature rise from 10 \({}^{\circ}\)C to 50 \({}^{\circ}\)C and an interval of temperature drop from 50 \({}^{\circ}\)C to 10 \({}^{\circ}\)C should be repeated several times, and the mean value of the COTE when the COTE difference in consecutive intervals is within 0.3 \(\times\) 10\({}^{-6}\)\({}^{\circ}\)C should be considered as the final COTE. Reference [20] provides a test method prepared by partially modifying the AASHTO TP 60 method. The most influential factor in the COTE of concrete is the type of coarse aggregate [10; 11; 12; 13] because coarse aggregate has the largest volumetric ratio in a concrete mix. [PERSON] [13] reported that the COTE was highest in concrete prepared using quartzite as aggregate and lowest in limestone concrete. It was also reported that the COTE increased with increases in the amount of SiO\({}_{2}\), which is consistent with the finding that quartzite has the highest SiO\({}_{2}\) content and limestone has the lowest. The COTE according to the type of aggregate is also consistent with the data reported by [PERSON] [10]. Although [PERSON] [10] reported that the COTE of sandstone was considerably high, it was found to be moderate in the study by [PERSON] [13] and in our previous study [1]. On the other hand, the data from FHWA [22] showed that the COTE was highest in chert, followed by sandstone and quartzite, with that of limestone being the second lowest and that of rholyite being the lowest. It is notable that the Eurocode [23] provided through experiments a COTE value for sintered fly ash, as aggregate, which falls between the lowest COTE values of marble and limestone. [PERSON] et al. [24] predicted the COTE of concrete by varying the shape of aggregate (circle, ellipsoid, square, rectangular) and using a self-consistent method; however, the effect of aggregate shape was found to be almost negligible. It is particularly known that the COTE of recycled concrete aggregate (RCA) is affected by not only the type of original virgin aggregate but also by the residual mortar (RM) attached to RCA [1, 22; 23; 24; 25]. Generally, the COTE value of mortar or RM is higher than that of concrete [10; 11; 13]. Few studies have been conducted to measure the COTE of RCA, and most previous studies have been focused on concrete pavement [22; 23; 24; 25; 26; 27; 28; 29; 30; 31; 32; 33; 34; 35; 36; 37; 38; 39] because the application of RCA is mainly concentrated on road applications. Previous reports showed that the COTE of RCA concrete generally increases as the replacement ratio of RCA increases [22; 25; 26; 27; 28; 29; 30; 31]. However, there have been various other reports recently indicating that the COTE of RCA concrete is retained [32; 33; 34; 35] or even decreases [36; 37; 38; 39] with increase of RCA replacement ratio. [PERSON] [26], ACPA [27] and NCHRPP [28] reported that the COTE of concrete increased to 30% with the increase of RCA replacement ratio. The test, performed with core specimens taken from 5 test sections of the Transportation Departments of four states in the United States, showed that the COTE of RCA concrete specimens was retained in 1 section but increased in 4 sections up to 9-23% [29; 30]. [PERSON] and [PERSON] [31] reported that when RCA was used at a ratio of 40%, the COTE of the concrete increased to 10%.