Key Engineering Materials Vols. 405-406

Abstract: The setting times and strength of cement substituting kiln dust-activated coal gangue for part of clinker was tested. The performance of sulphate resistance and restraining alkali silica reaction (ASR) of cement with 30% kiln dust-activated coal gangue was studied. The results indicate: the setting times of cement mixed with kiln dust-activated coal gangue is delayed and the early strength and later strength of cement with 10% kiln dust-activated coal gangue is improved to some extent, but the strength is reduced with farther increasing the content of kiln dust-activated coal gangue that replaces clinker, and obviously decreased when content of kiln dust-activated coal gangue is 30%; the performance of resisting sulphate of cement with 30% kiln dust-activated coal gangue is better enhanced; ASR is restrained to some extent.

Abstract: High performance concrete (HPC) with a water/cement ratio (w/c) of 0.32 and different lightweight aggregate (LWA) contents (0%, 25%, 50%, 75%, 100%) were prepared, and the influence of LWA on concrete frost-resistance and impermeability at different ages were studied, as well as the hydration degree, hydrated product, pattern and pore structure of the paste around aggregate. The results show that, by replacing normal weight aggregate (NWA) with 50% and 100% volume contents of pre-wetted LWA respectively, the chemical bound water of the cement paste surrounding aggregate are increased 12.1% and 22.7% as compared to concrete mixed without LWA. And at 28 days, lightweight aggregate concrete has the highest Ca(OH)2 content, whereas the 90-day Ca(OH)2 content of normal weight concrete is the highest. This proves that, with the increase of LWA content in concrete, both of the internal curing effect of pre-wetted LWA and secondary hydration effect of fly ash (FA) are strengthened, this can also be verified by the SEM study. Furthermore, the pore structure of the cement paste around aggregate can be improved consequently. The performance of frost-resistance of HPC can be improved by mixing LWA, the 90 day-frost-resistance of lightweight aggregate concrete is about 2.5 times of that of concrete mixed without LWA. The influence of LWA on the impermeability of HPC is different from normal concrete. When LWA content is more than 50%, the HPC impermeability decreased obviously, however at later age the difference between them becomes minor.

Abstract: The workability, strength and modulus of elasticity, drying shrinkage and creep, and chloride ion permeability as well as freeze-thaw resistance of the C60 high Performance concretes (HPCs) with manufactured sand (MS) containing crushed limestone dust in percents ranging from 3.5% to 14% were experimentally investigated. The results were compared with those of river sand (RS) concrete. In addition, the effect of clay amounts at 3% and 5% in MS on properties of C60 HPCs was also investigated. The results showed that expect for the creep, the other performances of C60 MS-HPCs with crushed limestone dust content of 7% to 10.5% were excellent or compared favorably with those of C60 RS-HPCs. The increment of clay content in MS obviously decreased workability, increased dry shrinkage and accelerated freeze-thaw destruction of C60 MS-HPCs, but didn’t affecting compressive strength and chloride ion permeability of the concrete. It was concluded that C60 HPC can be made with MS with a high content of crushed limestone dust but the amount of clay in MS should be controlled to a low limit.

Abstract: This paper investigated the mechanical properties, workability, autogenous shrinkage, drying shrinkage and durability of the high performance combined aggregate concrete with the coarse aggregate replaced by the lightweight aggregate in the volume fraction from 0% to 50%. The results demonstrated that the fresh concrete with the lightweight aggregate volume fraction of 10% and 30% had good workability, but degrade with a high volume fraction of 50 %. The hardened concrete with 10% and 30% lightweight aggregate replacement had similar compressive strength and splitting tensile strength comparing to the reference concrete without adding lightweight aggregate. The concrete with 50% lightweight aggregate replacement showed decreased compressive strength and splitting tensile strength. The concrete adding lightweight aggregate exhibited less autogenous shrinkage and drying shrinkage than the reference concrete without adding lightweight aggregate. The autogenous shrinkage and drying shrinkage increased with the increasing lightweight aggregate volume fraction. The concrete containing lightweight aggregate showed good durability after 200 freezing and thawing cycles, but the chloride permeability efficiency of concrete decreased.

Abstract: Effects of fly ash and ground granulated blast-furnace slag (GGBFS) on workability, strength, volume stability and durability of HSC are investigated. Results show that fly ash and GGBFS can improve the workability, increase the later strength of high strength concrete (HSC) remarkably, and reduce the brittleness. In addition, the ameliorative effect of GGBFS on HSC brittleness is more remarkable. With the increase of fly ash and GGBFS, the early elastic modulus of HSC reduces. The elastic modulus is similar to the controlled sample when the load is applied after 60d curing. The fly ash and GGBFS can improve HSC’s resistance to chloride ion penetration significantly. However, the effects of fly ash and GGBFS on freezing-hawing resistance of HSC are not obvious. Besides, the fly ash will reduce freezing-hawing resistance of HSC only when the content of mineral powder is up to 36%.

Abstract: The influences of fly ash, phosphorus slag powder and slag powder on the chemical shrinkage were researched in this paper. The results indicated that chemical shrinkage of cement paste was mainly relative to the mineral composition of cement, and three kinds of admixture could all make chemical shrinkage of cement paste reduce in early stages, but the chemical shrinkage of cement paste increased in later stages after mixing slag powder and phosphorus slag powder, and the activity of slag powder was higher than phosphorus slag powder, and fly ash could be used to inhibit chemical shrinkage of cement paste. The prediction model of chemical shrinkage of cement based materials was established.

Abstract: Modern concrete is more than simply a mixture of cement, water and aggregates; it also contains more and more mineral components, chemical admixtures, so the problem of concrete cracking will be more complicated. This paper mainly discussed the relationship between the character of various raw materials and the crack resistance of concrete. In order to improve the crack-resistant and durability of concrete, the technology for selecting raw materials of crack-resistant concrete is put forward.

Abstract: Recently, blast furnace slag, fly ash and limestone powder are increasingly used as blending materials in producing concrete. The use of these materials not only has economical and environmental advantages, but also improves the mechanical properties, durability and workability of concrete. In this paper, the results of experimental investigations on the evolution of hydration heat and the development of microstructure of Portland cement blended with blast furnace slag, fly ash or limestone powder are presented. These results show that three blending materials accelerate the hydration of Portland cement, but result in less heat release during the first 72 hours. The Portland cement with blast furnace slag has a denser pore structure than the others.

Abstract: Volume change of super high strength and high performance concrete with different binder-aggregate ratios and different curing conditions were investigated in this paper, and the volume changes of cement paste and mortar were also tested. The results indicated that the change of cement paste was much higher than mortar and concrete under the same curing conditions；the curing condition has a obvious influence on the volume change; there was a moisture swell for the water curing concrete; the specimens with limestone powder have smaller volume change than those specimens without limestone powder. The volume change mechanism was explained, and the effect of limestone powder on the volume change was also discussed.

Abstract: The paper investigates the volume shrinkage of different cementitious materials. The results indicates the type and fineness of cement have significant effect on the volume stability of hardened paste, namely, the concrete with higher fineness cement has worse volume stability. The addition of mineral admixtures makes the volume stability of cementitious materials become complex. The mineral admixtures of high quality can reduce the shrinkage of hardened paste, and the duality system of cement incorporating fly ash have better volume stability than the ternary system of cement incorporating fly ash and slag powder.