Understanding the behavior of recycled aggregate concrete by using thermogravimetric analysis

The physio-chemical changes in concrete mixes due to different coarse aggregate (natural coarse aggregate and recycled coarse aggregate (RCA)) and mix design methods (conventional method and Particle Packing Method (PPM)) are studied using thermogravimetric analysis of the hydrated cement paste. A method is proposed to estimate the degree of hydration (\alpha) from chemically bound water (W_{\mathrm{B}}). The PPM mix designed concrete mixes exhibit lower \alpha. Recycled aggregate concrete (RAC) mixes exhibit higher and \alpha after 7 d of curing, contrary to that after 28 and 90 d. The chemically bound water at infinite time (W_{\mathrm{B}\infty }) of RAC mixes are lower than the respective conventional concrete mixes. The lower W_{\mathrm{B}\infty }, Ca(OH)₂ bound water, free Ca(OH)₂ content and FT-IR analysis substantiate the use of pozzolanic cement in the parent concrete of RCA. The compressive strength of concrete and \alpha cannot be correlated for concrete mixes with different aggregate type and mix design method as the present study confirms that the degree of hydration is not the only parameter which governs the macro-mechanical properties of concrete. In this regard, further study on the influence of interfacial transition zone, voids content and aggregate quality on macro-mechanical properties of concrete is needed.