Key Engineering Materials Vols. 629-630

Abstract: It analyzed the performance, mechanical properties, volume stability, microstructure of hydration cementitious material of C60 self-compacting expansion concrete, which dependent on CSA to expansive ettringite source for the expansion. Results suggest that on the same curing conditions, C60 self-compacting concrete with the water-cement ratio of 0.32 admixture CSA expansive agent can effectively control the shrinkage of concrete, so that it is slightly inflated. The dosage of CSA expansive is higher, early strength of C60 self-compacting concrete is lower and its late strength declines small. It is affected little for the slump and extended degree of concrete under the superplasticizer by the expansive agent. SEM results show that CSA expansion agent can improve the pore structure of hydrated cement paste system with low water-binder ratio. The gel phase after hardening has good compactness and ettringite needlelike crystals mostly distribute at each interface layer.

Abstract: This article prepared a new type PVA fiber with large diameter by plasticizing melt spinning method, which instead of traditional wet-spinning or gel-spinning method. The mechanical properties and microstructure of fiber were characterized by tensile instrument respectively and SEM. Then, the PVA fiber was used in cementitious composites after surface sizing. The test result shown that: the melt-spinning PVA fiber could achieve stress-strain hardening in ECC system, and appeared multi-cracking phenomenon, the flexural deflection and strength is not worse than the Japan Kurary PVA fiber. Finally, the PVA has an advantage in price.

Abstract: s. The mechanical and durability properties of cement mortars with colloidal nanosilica (CNS) were investigated experimentally. Reference mortar with a low water-to-cement ratio of 0.30 was used in this study. The influence of CNS was evaluated by adding 0.5, 1.0, 1.5 and 2.0% of CNS by weight of cement. CNS was first stirred in the mixing water for 2 minutes before added to cement and sand. Superplasticizer was used to maintain the same flowability. Results showed that the compressive strength consistently increases with higher dosage of CNS at all the curing ages, due to both hydration acceleration and pozzolanic reaction. With the increase in CNS, the migration coefficient and water sorptivity consistently decreased; with 2% of CNS, the migration coefficient and water sorptivity were reduced by 45% and 30% respectively in comparison with the reference mortar. The improved durability could be explained by the reduction and refinement in the porosity, which can be attributed to nanofiller effect and pozzolanic reaction of nanosilica. Furthermore, the addition of CNS could reduce the drying shrinkage by densifying the microstructure in the cement paste, which has not been reported previously.

Abstract: The extraction of china clay in the South West of the UK generates waste in a mass ratio of 1:9 for china clay: waste. Currently, part of the coarser waste, “stent” and sand named “china clay sand” (CCS) in this study, is used as building stone or secondary aggregate in concrete and asphalt but the finest waste fraction, called “mica” waste, is used only for the restoration of old quarries. Looking for innovative solutions for the needs of a new Eco-town in the UK, and with regard to uses commercially applicable to construction and of low environmental impact, the china clay waste is being studied as an aggregate in alkali-activated cements (AAC). Aiming to replace primary aggregates with wastes in low risk construction materials, a series of AAC concrete based on a 50% GGBS and 50% fly ash (FA) blend and an equivalent Portland concrete series were produced. In the mixes the primary aggregate was steadily replaced by forms of the waste and tests in compression showed a decreasing trend in strength accordingly. The two series of concrete follow approximately the same ratios of decrease although in absolute values the AAC series reached higher range of strengths on the 28 day compared to the Portland series. While the use of CCS did not have any negative impact, the addition of mica decreased the strength up to 25% more.

Abstract: The microbead modified super sulfate cement (SSC) was employed to prepare C60~C80 concrete, this work emphasis on mechanical properties and micro-mechanism, besides, the service behaviors of fresh concrete was tested. The SSC concrete mechanical properties influenced by particles size of microbead, slag and gypsum were discussed. Mechanisms of mechanical properties changes were elaborated from micro, meso and macro scales, mechanical model was established and relevant rules of mechanical properties development were obtained. Experiment results show that compressive strength increased with the largerer specific surface area of microbead, slag powder and gypsum. There was a promoting effect for SSC concrete hydration reaction by appropriate dosage (10%~20%) of microbead, which had prominent interstitial effect and system with excellent gradation, and fresh concrete workability was significantly improved. The compressive strength—curing ages model of high strength SSC concrete was established by half value intensity index, which coincide well with measured values. Key words: super sulphated cement concrete, microbead, mechanical properties, mechanical model, specific surface area

Abstract: Abstract: The same amount of mixture ratio of cement, replacing a part of fly ash with a certain amount of mud to research about the workability of fresh concrete and the effect of the mechanical and shrinkage properties of hardened concrete. Test's results show: The different kinds of mud lead that the fluidity of the fresh concrete and the strength of hardened concrete are different. The influence of sand mud is lighter than planting mud on the fluidity and strength of concrete. The compressive strength of concrete decreases and the early shrinkage increase with an increase of mud replaced the fly ash.

Abstract: The effects of the size and volumetric content of rubber powder on properties of concrete, including flexural strength, compressive strength and permeability, were studied in this paper. Two different particle sizes (20 meshand 60 mesh) of rubber powder were chosen to replace the sand with volume content of sand as5%, 10%, 15%, 20%, 25%, 30% respectively. The results showed that both flexural and compressive strength of concrete, especially compressive strength, decreased with the increase of rubber content. Moreover, the smaller the particle of rubber powder, the greaterer the strength of the concrete, which was not obvious as effect of rubber powder content on the strength of concrete. The impermeability of concrete increased with the increase of rubber powder content. The electric flux of concrete with 30% rubber powder reduced to about 900 C, which was only 1/5 of that with 5%. At the same content, smaller rubber particle has positiveeffects on the impermeability of concrete. Keywords: rubber concrete,rubber powder, compressive strength,flexural strength, permeability performance.

Abstract: In this paper, the influence of water cement ratio, prewetting degree of lightweight aggregate, flyash content and air content on the internal relative humidity (IRH) and drying shrinkage of lightweight aggregate concrete (LAC) were studied using a relative humidity sensor and drying shrinkage apparatus. Results showed that the IRH of concrete decreased rapidly at early age and slowed down at late age, and prewetting lightweight aggregate could compensate the loss of IRH. The effect of compensation could be enhanced with the increasing of prewetting degree of lightweight aggregate, and the addition of flyash retarded the decrease of IRH at early age. The drying shrinkage of LAC increased quickly at early stage and it slowed down to the even after 60 days or longer age. Furthermore, the drying shrinkage of LAC increased with increasing of water cement ratio. The effect of air content on the drying shrinkage of LAC was limited at early stage. However, at the late stage it grew at different level with increasing of air content. By raising the prewetting degree of lightweight aggregate, mixing with proper dosage of flyash, the shrinkage rate of LAC can be reduced markedly. Key words: lightweight aggregate concrete, internal relative humidity, drying shrinkage, prewetting degree, flyash.

Abstract: The soda residue pollutes the environment because of high contents of alkali ion and choleric ion in it. So how to treat the soda residue is an urgent problem to be solved. The mineral admixtures are added in traditional inorganic binder to improve the strength performance of inorganic binder stabilized materials and decrease the negative effect of soda residue is studied. And the results as followings: (1) Soda residue has different activated effect on mineral admixture; (2) Mineral admixture replace the cement with same dosage can improve the unconfined compressive strength greatly to meet the requirement of standard; (3) The choleric ion leaching rates of cement-mineral admixture-soda residue stabilized stone chip decrease with time. Mineral admixture has a better immobilization effect on the chloride ion except fly ash before 90d; (4) Ground granular blast-furnance slag is the best material to improve the strength performance of inorganic binder stabilized materials and decreases the negative effect of soda residue.

Abstract: For their remarkable properties, carbon nanotubes (CNTs) are considered as promising candidate for next generation of high performance and functional cement-based composites in 21st century. The paper focuses on the dispersibility, mechanical property, durability, conductivity and piezoresistivity properties of CNTs reinforced cement-based materials. A homogenous CNTs-suspension was obtained using the method which combined ultrasonic processing with mechanical stirring, electric-field introduction and surfactant decoration. The low weight fraction of CNTs improved the mechanical properties of CNTs/cement composites. The compressive strength and toughness were correspondingly improved. The added CNTs improved the sulfate attack resistance and impermeability properties of the prepared CNTs/cement mixes. Meanwhile, the added CNTs improved the pressure-sensitive, conductivity and electromagnetic absorption properties of the prepared mixes, which laid a foundation of multi-functional concrete and structure. It concludes that the key issue for CNTs/cement composites is the dispersibility and the compatibility of CNTs in cement matrix. The solving solutions are put forward. In the meantime, the further research prospects in this research field are forecasted.