[en] Tsinghua University started to test the biaxial and triaxial compressive concrete strength and deformation since 1983. Test results of biaxial and triaxial compressive concrete strength are analyzed. A concrete failure criterion is suggested and is compared with others. Biaxial compressive stress-strain relationships under different load ratios are investigated. (orig./HP)

[en] High early strength concrete is fundamentally developed to provide a better solution to early housing and rehabilitation projects. Investigation in this project focuses primarily upon various industrial based accelerating admixtures which are dispensed in concrete mix in various dosages to obtain a high efficient mix. The specimens were casted and subjected to chemical and moisture curing. Fresh concrete properties like slump for workability and penetration resistance to analyse very early strength were done. Compressive strength at 1, 3, 7, 28 days were observed in order to identify the optimum dosage of accelerating admixtures. The result obtained showed that the type Y accelerator and chemical curing are the most suited to achieve high early strength concrete. (paper)

[en] The polyurethane composites were prepared by a one-pot free-rising method with Melamine cyanurate (MC) and Cloisite 20A additives. Flame-retardant and mechanical properties of the foams were investigated. The vertical burning test showed that PUF composite loading 15 wt% MC was reached V0 classification of V-rating. Limiting oxygen index (LOI) test revealed that the PU foam changed from an especially flammable material (LOI = 18.4 %) to a flame-resistant material (LOI = 24.1 %) upon adding 25 wt% MC. However, the presence of MC reduced the compressive strength of the foam. In this report, we demonstrated the incorporation of organoclay and MC into PUF could improve the flame retardancy and the compressive strength of polyurethane foam. (author)

[en] To investigate the influence of water-cement ratio on the fluidity and mechanical strength of geopolymer grouting materials, the change of fluidity, compressive strength and flexural strength of road geopolymer grouting material with different water-cement ratio were tested. The results showed that the fluidity of geopolymer grouting material was enhanced while the compressive and flexural strength decreased with the increase of water - cement ratio. The optimum value of water-cement ratio was in range (0.39-0.42). The road geopolymer grouting material had the better fluidity and the strength requirement of reinforcement if the main constituent materials was not changed. (paper)

[en] Steam curing process is generally adopted for precast concrete products to improve productivity. For setting reasonable production cycles and selecting economical formulation, it is important to predict the strength of mortar / concrete at early stage. Compressive strength estimation by the Maturity method is being widely used in conventional research. However, it is pointed out that accuracy is relatively low for estimating the strength of concrete under steam curing condition. Therefore, in this study, a relation between effective material ages based on the Maturity and Arrhenius’s law and both initial and long-term strength were evaluated. As a result, it was confirmed that the Arrhenius's law shows higher estimation accuracy than the Maturity method. Furthermore, it was confirmed that the prediction method using effective material ages based on the Arrhenius’s law which takes the activation energy into consideration has higher estimation accuracy. (paper)

[en] To determine the relationship between compressive strength and flexural strength of pavement geopolymer grouting material, 20 groups of geopolymer grouting materials were prepared, the compressive strength and flexural strength were determined by mechanical properties test. On the basis of excluding the abnormal values through boxplot, the results show that, the compressive strength test results were normal, but there were two mild outliers in 7days flexural strength test. The compressive strength and flexural strength were linearly fitted by SPSS, six regression models were obtained by linear fitting of compressive strength and flexural strength. The linear relationship between compressive strength and flexural strength can be better expressed by the cubic curve model, and the correlation coefficient was 0.842. (paper)

[en] A type of cost-effective and very high strength concrete (VHSC) with 28-day compressive strength of 100-150MPa is developed for applications in concrete-encased steel composite column constructions. This paper experimentally investigates the structural behaviour of VHSCencased steel composite columns based on a series of pure compression and eccentric compression tests. It is found that such high-strengthcomposite column exhibits brittle post peak behaviour and low ductility but with acceptable compressive resistance. Throughout the tests, the main failure of VHSC encased column under compressive load is brittle spalling of concrete followed by local buckling of the reinforcement bars. The splitting and slippage may occur between concrete and steel section due to bending downward action. The confinement effect by the shear stirrups designed based on normal reinforced concrete codesmay not be sufficient. Composite column subjected to initial flexural cracking due to end moment load with large eccentricity may experience degradation in the stiffness and ultimate resistance so that plastic design resistance may not be achieved. Analytical studies show that the N-M interaction model based on current design codes may over-predict the combined resistance of the composite columns. Therefore, a modified elastic-plastic design approach based on strain compatibility is developed to evaluate the compressive resistance of concrete encased composite columns. The validation against the test data shows a reasonable and conservative estimation on the combined resistance of VHSC encased composite columns. (Author)

[en] The effect of seaweed such as Eucheuma Cottonii (gel) and Gracilaria Sp. modified mortar on the properties of sustainable concrete was investigated. Pre-experiment and main-experiment was conducted to carry out this study. Pre-experiment was conducted to study the compressive strength of the sustainable concrete. The main-experiment studied the compressive and splitting strength. Results showed that seaweed modified mortar yielded satisfactory compressive and splitting strength of 30 MPa and 5 MPa at 28 days. (paper)

[en] Experimental investigation on the relationships between corrosion of reinforcement and concrete for the bond strength in pullout test and flexural test has been conducted to established the maximum strength. The reinforcing bars used in this study were rusted for four, eight and twelve months, it is cleaned for the eight and twelve months before embedded in concrete cubes for pullout test and concrete beams for the flexural test. The first component for experimental to make reinforce bars exposed to weathers and the parameter included 20 N/mm² concrete compressive strength. The diameters of reinforcing bars 12 mm, 16 mm and 25 mm used for tensile test and pullout test. 8 mm, 12 mm, 16 mm and 25 mm for flexural test. Tensile test carried out according to ASTM A615 16 and MS146:2006. Pullout test conducted according to ACI and BS 1881 Part 207:1992. Flexural test performed according to ACI and BS 8110 Part 1:1985, BS 1881 Part 109:1983 and BS 1881 Part 118:1983. All specimen’s workmanship for reinforcement carried out according to BS 8110 Part 1: 1985 and to support this thesis based on previous literature review. (paper)

[en] Highlights: • Zircon up to 10 g/100 g metakaolin improved microstructure and mechanical properties. • No new phases were formed upon the addition of zircon. • Zircon didn't participate in geopolymerization reaction. • Zircon entered between polysialate networks and formed a rigid microstructure. • Higher content of zircon (15 g/100 g kaolin) lowered the compressive strength.