Key Engineering Materials Vols. 302-303

Abstract: The characterization of hardened concrete was analyzed by testing the weight change of water absorption. A simple testing method is submitted and discussed in this paper. As one of the test results, it was reported that the relationship between weight change (at) and time (t) of water absorption test would be well fitted with at=(α×t)/(β+t). Based on the result, laboratory studies of a water absorption test were carried out. Test results were discussed for estimation of mix proportions, compressive strength, and carbonation of different kinds of concrete.

Abstract: The aim of this paper is to provide the credible evidence for existing theory. Rc、Rpl、 Rl and body shear strength of roller compacted concrete (RCC) are investigated. According to the database of Chinese RCC projects, eight regressive equations were set up by using the method of correlation analysis. Including relations for Rc、cementitious material/water ratio and content of fly ash, increasing rate of Rc and age, increasing rate of Rpl (or Rl ) and age, Rpl (or Rl ) and Rc, Rpl and Rl and body shear strength and age.

Abstract: Based on available test data and fracture criterion, by using probability fracture mechanics and mathematical statistical method, the distribution feature of fracture toughness, IC K , of interface between coarse aggregate and hardened cement mortar is analyzed, and a method of defining the least number of specimens for testing fracture toughness is provided. Weibull distribution or lognormal distribution is often used to analyze lifetime problem, so the two models are preferentially considered. The analysis shows that the fracture toughness conforms to lognormal distribution with degree of confidence g =0.9, relative deviation d =0.05 and the least number of specimens of 13. The study results can be used in the probability fracture analysis and construction quality control of interface between coarse aggregate and hardened cement mortar.

Abstract: Reactive powder concrete (RPC) is a new kind of ultra-high strength and upper ductility concrete first developed in 1990’s in France. In this paper, the RPC mixture proportion is optimized and its mechanical properties, such as compressive strength, flexural strength, elastic modulus, and its durability, are tested and discussed. Based on the optimal mixture proportion, four simply supported plain RPC beams (without reinforcement bars) are made and tested. The mechanical properties of plain RPC beams, including section deformation, load-displacement relationship, failure forms, crack distribution, crack extension, and ultimate flexural capacity, are discussed. It is concluded that RPC is an excellent material with high strength and durability. Steel fiber is important both to control the crack extension and to enhance the ductility of RPC beams.

Abstract: Hardened cement paste and concrete are porous materials. Most engineering properties of hardened cement pastes and concrete, such as strength, shrinkage, permeability, etc., are influenced or controlled by their pore structure characteristics. The ingress of chloride ion into concrete can cause steel corrosion and damage of steel reinforced concrete structure. This paper reviews the pore structure characteristics and transport mechanisms of chloride ion, such as hydrostatic advection, capillary suction, diffusion, thermal migration and electrical migration, in hardened cement pastes and concrete.

Abstract: In this paper, full-range compression tests were conducted on prisms of Old concrete, New-Old concrete and High-Performance Rapid Repair Concrete (HPRRC) prisms The complete stress-strain curve of HPRRC incorporating PFAC (pulverized fly ash composite), Old concrete and New-Old concrete were obtained and compared with each other. The essential uniform deformation capacity of three kinds of concrete was verified with the experimental results. At the same time, the unified numerical expressions of the compressive complete stress-strain curves of the three kinds of concrete are put forward. The theoretical curves from calculation are in good agreement with the experimental curves.

Abstract: A novel phosphate bonded magnesia cement was developed recently, which sets quickly and develops high strength in the early ages. In the present research, the physical and mechanical properties, hydration products, and microstructure of the new cement were investigated. The new cement was mainly consists of dead burned magnesia, phosphate and fly ash. The results showed that it not only has high early strength, but also has high long-term strength. Interestingly, the strength of the cement increase with the content of fly ash, from 10 % - 40 % by weight. The hardened cement paste has a dense microstructure, low open porosity and water sorptivity due to the low water to binder ratio. The reaction products after hydration of the cement includes struvite mineral and amorphous species.

Abstract: Cement mortar of high damping ability has been maded by using styrene-acrylate emulsion as an admixture. The addition of styrene-acrylate emulsion causes the loss tangent of plain cement mortar to increase at all temperature (-30-30 °C) and frequencies (0.1-2.0 Hz), and the loss tangent increase is particularly large at 15-30 °C, even up to 0.25 at 30 °C and 0.5Hz due to the glass temperature of styrene-acrylate emulsion, although the storage modulus of cement mortar with this admixture decreases at all temperatures and frequencies, however, for the loss modulus, which serves as an comprehensive figure-of-merit for the vibration reduction ability, styrene-acrylate emulsion may dramatically increase it. The X-ray diffraction (XRD) and infrared (IR) spectrum analysis have provided evidence that styrene-acrylate decelerates the hydration of cement paste.

Abstract: Reactive powder concrete (RPC), which is a new cement-based composite material with ultra-high strength, low-brittleness, excellent durability, is adopted to make well covers. In addition, static loading tests of the well covers are carried out. The test results show that the loading capacity of the RPC well covers can meet the requirements for different situations, such as the special roads, the city motorway, footway, various parking places, etc.

Abstract: The influence of GGBS (ground granulated blastfurnace slag) on concrete compressive strength is experimentally investigated in this paper. By bond strength experiment of GGBS concrete with reinforcing steel bar, the influence of GGBS mixture proportioning on bond strength is studied. The result indicates that, with an increase replacement percentage of GGBS, the bond strength between concrete and steel bar will decrease, and the depressed magnitude relates to the dosage of slag powder and type of steel bar. The studies provide a reference for the exploitation and application of GGBS concrete. As known to all, blastfurnace slag is a kind of industry waste produced by blastfurnace puddling. A great deal of research has been conducted on the characteristics of slag powder. The improvements of GGBS on the concrete composites are widely accepted. Studies on GGBS concrete bring remarkable social and economical benefits such as: reducing cost of per cube concrete; improving concrete performance and making full use of industry waste residue. The influence of GGBS mixture proportioning on concrete compressive strength and the bond characteristics between concrete and steel bar is experimentally studied in this paper.