Papers by Keyword: Recycled Cement

Abstract: The recycled cement production, utilizing all components of the waste concrete without separation treatment as raw materials, provides an effective method for the high value-added resource recovery of waste concrete. However, as fine aggregate (sand) is the main siliceous component in the recycled cement raw materials prepared from waste concrete, its excessive high-crystalline silica content negatively impacts the burnability of raw meal and the property of clinker. By comparing and analyzing the results of burnability test, XRD patterns of clinker and compression strengths of cement paste, this paper attempts to explore the effect of F-S mineralizer on the calcination of recycled cement clinker produced from waste concrete. It could be concluded that F-S mineralizer has a significant improvement on the burnability of recycled cement raw meal, and the f-CaO content decreases with the mineralizer dosage rising. Moreover, in the case of calcination temperature at 1350°C, F-S mineralizer contributes to the enhancement of compression strength of recycled cement paste. Early high-strength minerals ( and C₁₁A₇⋅CaF₂) are prime motivator to early strength increment, while long-term strength benefits from mineralizer’s improving on hydration activity of silicate mineral in clinker.

Abstract: Utilizing construction waste, mainly waste concrete, to produce recycled cement, provides possibility for realizing the closed circulation between concrete and cement, which is an effective way for sustainable development of cement and concrete industry. Waste clay brick (WCB) and its surface-coated waste mortar are inevitably introduced into the raw meals while waste concrete is used in cement production. So on the basis of the composition characteristics of construction waste, considering of optimizing the performance of recycled cement and improving the adaptability of recycled cement to complex raw material, it's necessary to study the effect of raw meal mixing waste concrete and WCB on sintering process and property of recycled cement clinker. Mixing waste concrete and WCB in three different proportions, the burnability of raw meal, clinker mineral composition, clinker mineral morphology and hydration characteristics of recycled cement have been studied in this paper. The results indicate, the presence of WCB is beneficial for the generation and development of silicate minerals; with increasing proportion of WCB, the content of f-CaO in recycled cement clinker rises, the structure of C-S-H gel from hydration product presents higher densification and the compression strength of 3d and 28d curing period are enhanced.

Abstract: The purpose of this study is to determine whether cementitous powder of waste concrete which is separated from waste concrete can be used as alternative raw material for limestone. Chemical composition of cementitous powder of waste concrete was actually analyzed and the experiment to measure the recovery of hydration of waste cementitous powder model was performed. As a result, hydration was recovered to the level at which it can be used as alternative raw material for limestone, but less than 10 % can be used due to mix of fine aggregate in less than 150μm which cannot be separated from cementitous powder. Therefore, development of technology to efficiently separate cementitous powder of fine aggregate is required to have the alternative material for limestone and effect for reduction of greenhouse gas.

Abstract: Adding part of granulated blast furnace slag(GBFS), steel salg(SS) , Desulfurization gypsum(DG), we can use Waste Cencrete（WC）as the main raw materials to directly produce uncalcined cement by grinding.With mix proportion 40%~50% of WC and curing in water, the 3d compressive strength of the cement can reach 10MPa.,the 28d compressive strength of the cement can reach 20~40MPa. XRD and SEM analysis show that, the hydration products of the cement are ettringite and C-S-H gel. Parts of WC involves in the hydration reaction, residual WC is wrapped by the hydration product as aggregate filler.