Hydration heat effect of cement pastes and mechanism of hydroxypropyl methyl cellulose ether （HPMC） and expanded perlite in cement pastes were studied by means of hydration exothermic rate, hydration heat amount, FTIR and TG-DTG. The results show that HPMC can significantly delay the hydration induction period and acceleration period of cement pastes. As mixing amount increased, hydration induction period of cement pastes enlarged and accelerated period gradually went back. At the same time, the amount of hydration heat gradually decreased. Expanded perlite had worse delay effects and less change of hydration heat amount of cement pastes than HPMC. HPMC changed the structure of C-S-H during cement hydration. The more amount of HPMC, the more obvious effect. However, EXP had little influence on the structure of C-S-H. At the same age, the content of Ca （OH）2 in cement pastes gradually decreased as the mixing amount increase of HPMC and expanded perlite, and had better delay effect than that single-doped with HPMC or expanded perlite when HPMC and expanded nerlite were both dooed in cement pastes.
Cellulose ethers are widely used to mortar formulations,and it is significant to understand the interaction between cellulose ethers and cement pastes.FT-IR spectra,thermal analysis and SEM are used to investigate hydration products in the cement pastes modified by HEMC and HPMC in this article.The results show that the hydration products in modified cement pastes were finally identical with those in the unmodified cement paste,but the major hydration products,such as CH（calcium hydroxide）,ettringite and C-S-H,appeared later in the modified cement pastes than in the unmodified cement paste.The cellulose ethers decrease the outer products and increase inner products of C-S-H gels.Compared to unmodified cement pastes,no new products are found in the modified cement pastes in the present experiment.The HEMC and HPMC investigation shows almost the same influence on the hydration products of Portland cement.
Recycled ceramic mixed sand（RCMS） was obtained by partially replacing ultra-fine sand with recycled ceramic coarse sand（RCCS）. The effects of RCCS replacement rate on the apparent density, workability, compressive strength and splitting tensile strength of recycled ceramic concrete（RCC） were investigated. In addition, the relationship between the water-cement ratio and compressive strength of RCC was also studied. The experimental results indicate that the reusing of recycled ceramic aggregate can improve the cohesiveness and water retentiveness of fresh concrete and benefit the mechanical properties development. When the RCCS replacement rate is not less than 40%, the mechanical properties of RCC are superior to those of the reference concrete. Moreover, when recycled ceramic medium sand was completely used as fine aggregate, the maximum increase in both compressive strength and splitting tensile strength were obtained, comparing with those of reference concrete, the increment ratio was 19.85% and 32.73%, respectively. The microscopic analysis shows that the using of recycled ceramic aggregate can meliorate distinctly the structure of the interfacial transition zone（ITZ） and increase the compaction degree of cement paste. Furthermore, an expression of the compressive strength of RCC and the cement-water ratio is regressed and gains a good linear relativity. It is an effective way to recycle waste ceramic, and the consumption of recycled ceramic aggregate could reach from 26.9% to 47.6% of the total weight of aggregate in producing concrete.
