The aim of this paper is to investigate mechanical properties and heat generation of concrete produced with a carbide lime (CL) and fly ash (FA) mixture as a new cementitious material without Portland cement. Two techniques were used to improve the strength of concrete: adding of NaOH into the new binder (1% by weight) and increasing the fineness of new binder. Microstructural mechanism in term of SEM microscopy, EDX analysis, and XRD patterns of CL-FA pastes were examined. The following properties of cement-free concrete were also examined: heat generation, compressive strength, elastic modulus, and splitting tensile strength. The results of microstructural revealed that the products of binder made from CL and FA were C-S-H and C-A-S-H phase types and the formations of C-S-H and/or C-A-SH were attributed to components of Al, Si, and Ca. The results also showed that the peak temperature rise of concrete made from CL and FA could be reduced by 30-36 degrees C from that of the OPC concrete. Regarding the mechanical properties of concrete, the technique of improving strength by increasing the fineness of new cementing material was the best method and could produce the 28-day compressive strength of 55.0 MPa. CL-FA concrete had elastic modulus and tensile strength similar to those of OPC concrete. Furthermore, the techniques to improve the strength of concrete had no significant effect on the elastic modulus and tensile strength of concrete since those properties were related to the compressive strength of concrete. Moreover, the concrete had a very low heat generation as compared to the OPC concrete. (C) 2017 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.