The Experimental Researches On Special Cement For Road Base Course And Concrete Surface With Slag As Main Component

With the rapid development of road construction, especially the highway construction in China, the researches and application of new materiales for road base courses and pavements have become one of the leading research projects. It has been found that with the addition of ground granulated blast furnace slag (GBFS), especially with large amount of GBFS in addition, the consumption of resources and energy as well as the greenhouse emissions will be reduced, and the faults of the ordinary Portland cement(OPC) will be improved. According to the requirements of road base and concrete surface road on cement features as big as possible , two most commonly used cementitious materials with slag powders as the main component have been developed.The new slag binder NSB43A and NSB43B of road base are chosen after the following three procedures: (A)The selection of the proper raw materials of road base materials such as GBFS and alkali calcium sulfur stimulate materials(cement, slaked lime,limestone, and gypsum), which is based on the consideration of the technical performances, construction requirements and economic factors. (B)The choice of the setting time and compressive strength as the main design index. (C)Relevant choices made in setting time, together with the compressive and flexural strength and contraction coefficient experiment. These two NSB both contain 75wt% GBFS. In NSB43A, 2wt% limestone is contained in its GBFS, whereas in NSB43B, 4wt%. There two slag binder NSB have been proved to be more suitable for road base course with their good performance of slow setting, better anti-crack and higher strength, resulting in economic benefits and environmental protection.Before the systematic research on such factors as GBFS, stimulate materials and the type and dosage of adjustable coagulant on the cementitious material technology performance, construction requirements and economical factors of pavement concrete , the following proper raw materials are chosen: GBFS, alkali calcium sulfur stimulate materials(cement clinker, limestone, gypsum), alkaline stimulate agent(Na2SiO3?9H2O and NaOH),and coagulation agents. Cement setting time, flexural tensile strength, cracking-resistance are taken as the main design index. As a result, six SRC projects have been recommended. The research of the pavement concrete surface of SRC indicates that with the use of adjustable coagulant and composite stimulate materials such as cement clinker, gypsum and limestone, a series of SRC can be designed. In the SRC projects, the amounts of GBFS and clinker dosage vary in comparatively larger ranges, with GBFS powder from 47~75wt% and clinker, 25wt% to 50wt%. These designs have turned out to satisfy cement road technical standard by using large amount of GBFS, producing pavement concrete of greater flexural tensile strength, ideal setting time and the higher compressive strength grade,all of which lead to favorable economic benefits and environmental protection.Based on the above-mentioned optimized compositions and with focus on the strength, anti-cracking performance and construction feature of the NSB stabilized soil,and SRC concrete's strength and durability, systematic research has been conducted in the indoor experiments on NSB stabilized fine-grained soil, gradation gravel and SRC concrete road performance. Fuzzy comprehensive evaluation method is also used in the experiments in analyzing NSB stabilized fine soil, NSB stabilized gradation gravel and P.O32.5R stabilized soil, SRC concrete and P.O42.5R concrete comprehensive performance in order to testify the feasibility of special road cement with the GBFS powder as the main component and to analyze the applicable occasions of NSB and SRC.Finally, XRD and SEM are employed in the micro-analyses on the newly developed binders and its stabilized soil: NSB43A, NSB43B and their reference material P.O32.5R, and on their hydro-products as well as the photographs of them at different ages. Furthermore, the experiments have also explored into the features of SRC, its hydro-products and corresponding micro-photograph.The study has delved into the reasons of pore bigger solution pH value of newly developed cement and hydration pruductions C - S - H gel lower Ca/Si using thermodynamic principle, in addition to the research of NSB and its stabilized soil, SRC strength mechanism. The photographs of the hydro-products indicate that the biggest differences between special slag cementitious materials and OPC lie in the fact that the former has the comparatively larger amount of AFt and contains little Ca(OH)2, and the latter has larger amount of Ca(OH)2 but little AFt.