Applied Mechanics and Materials Vols. 405-408

Abstract: A review of current worldwide researches on the durability of concrete was presented. Porosity and water content of concrete changing in wet-dry cycles were introduced, the failure mechanism of freeze-thaw and carbonation and the relation with pore structure, as well as its interaction influencing factors. Some key problems to be further studied were proposed on the basis of the research achievements of leaching.

Abstract: To solve the problem of cracks developing on thin-walled concrete structures during construction, the authors expound on the causes of cracks and the crack mechanism. The difference between external and internal temperatures, basic temperature difference and constraints are the main reasons of crack development on thin-walled concrete structures. Measures such as optimizing concrete mixing ratio, improving construction technology, and reducing temperature difference can prevent thin-walled concrete structures from cracking. Moreover, water-pipe cooling technology commonly used in mass concrete can be applied to thin-walled concrete structures to reduce temperature difference. This method is undoubtedly a breakthrough in anti-cracking technology for thin-walled concrete structures, particularly for thin-walled high-performance concrete structures. In addition, a three-dimensional finite element method is adopted to simulate the calculation of temperature control and anti-cracking effects f. Results show the apparent temperature controlling effect of water-pipe cooling for thin-walled concrete structures.

Abstract: Aiming at the problem that the permeability, bond performance and waterproof property of the layer-penetration oil used in the highway engineering is poor, this article puts forward and develop a kind of high-permeability emulsified asphalt layer penetration oil. This layer-penetration oil is the emulsified asphalt that mixed by the tyre pyrolysis asphalt and the SK 90# asphalt, added by penetrant, emulsifier and curing agent, emulsified by the colloid mill. Some indoor test for this layer-penetration oil have been done. All these tests show that the layer-penetration oil has good permeability and good bond performance after the infiltration of the grassroots demulsification. So we can see that it has excellent engineering value and it is worthy of popularization and application.

Abstract: This paper reported a new type MDF absorber of high absorption and Broadband was successfully prepared, according to the Electromagnetic Wave Absorbing Theory, by means of the theoretical design and simulation analysis by using MDF as the dielectric material and And with the resistance film composite. Results shown that the resistance of resistive film was 195Ω/□, the monolayer combined sample with thickness as 1.4cm in 2~4 GHz frequency bands, the range of absorbing over -20dB could achieve 50%, and all absorption could exceed -15dB in the whole S-band, the maximum absorption peak was -25dB, moreover, the absorption bandwidth of MDF was more than λ/4 Type EWM-absorber. The new materials could be used to improve residential electromagnetic environment and control pollution.

Abstract: Inorganic polymers using slag as cementitious materials have the advantage of a short setting time, high early strength, but the sensitivity of the reaction rate to temperature and the likelihood to subsequently crack, which leads to reduction of strength, limit its application. This article, by configuring different proportion of fly ash and slag, studied its dry shrinkage with the different kinds of activator, the effects of fly ash on the hydration heat release curves, differences of setting time and strength with different configuration, and then explored the effect of fly-ash in inorganic polymer. Experiments had shown that through rational configuration, the addition of fly ash can effectively reduce the rate of heat release and the amount of heat, meanwhile can solve the problem about short setting time of alkali-activated cementitious materials without reducing its strength.

Abstract: As a new environment-friendly fiber material, the basalt fiber has been used in engineering construction to a certain extent. Through the tests for compressive strength and split tensile strength of concrete matrices in different ages, the reinforcement of basalt fiber for concrete was explored in this paper. As shown by the test results, the mixture with basalt fiber would efficiently enhance the ductility of the concrete being broken, and improve the compressive strength and split tensile strength of concrete matrices in different ages, in which the compressive strength of concrete in the age of 3d and the split tensile strength of concrete in the age of 28d were improved more significantly, by 9% and 19% respectively. The test analysis results can be used as a reference for application of basalt fiber in concrete projects.

Abstract: Because of low strength, the expanded perlite insulation boards application in building energy saving is restricted. This paper discuss change rules of the expanded perlite insulation board apparent density and mechanical strength with adjusting the amount of sodium silicate, pressing pressure, heating system. It turned out that good thermal insulation performance and high strength expansion perlite insulation board is prepared by mass ratio of 2.5:1 of 30% of the content of solid sodium silicate solution to expanded perlite, 0.38MPa of pressing pressure and 105°C condition of heating temperature.

Abstract: The synthesis process of polycarboxylate superplasticizer (PCE) by bulk polymerization was investigated. Compared with BPO as initiator, PCE prepared by using AIBN as initiator exhibited better cement paste fluidities. PCE using isopentenyl polyethylene glycol (TPEG) or isobutenyl polyethylene glycol (IPEG) as macromonomer showed excellent fluidities and retaining properties at 80°C and 75°C, respectively. The fumaric acid was more suitable to copolymerize as the third monomer than maleic anhydride. The molecular weight measurements showed that the characteristics of molecular weight and its distribution for all the synthesized samples were in accordance with their cement paste fluidities. The solid-state PCEs can be conveniently dissolved into water to prepare PCE solution with arbitrary concentration, and still with good cement application performances.

Abstract: Ultra-high strength concrete (including the coarse aggregate of over 5mm), with high compressive strength and strong durability, is regarded as a new-type building material that could economize on raw materials, land and energy and the development trend of concrete technology both at home and abroad. However, the large consumption of binding materials, low water-binder ratio and the viscous mixture are prone to give rise to the inferior pumping capacity, pipe blockage and pipe break, thus preventing its massive application in the real projects. Therefore, through the design of reasonable mixture ratio, this paper makes up and produces the pumping ultra-high strength concrete of over 100MPa that contains coarse aggregate by adopting the compound design of mineral admixtures, such as slag powder, fly ash and ganister sand so as to optimize the relevant parameter of the mixture ratio. Finally it comes to the conclusion that while making up the ultra-high strength concrete of over 100MPa, it is much more reasonable to appropriately add the mixing amount of the mineral admixtures, increase the water-cement ratio and decrease the water-binder ratio.

Abstract: In order to understand the law on concrete degradation induced by microwave irradiation, the experimental research is conducted in which the following works are completed. At first, the different concrete specimens are exposed to microwave of various power levels for various time periods, and then some specimen irradiated by microwave are cooled in air, the other cooled by spraying water. After that, the tensile strengths of the heated and unheated specimens are measured with Brazilian test method. According to the test results, the reduction of tensile strength of plain concrete and steel-fiber reinforced concrete induced by microwave irradiation is analyzed, and the relations between the tensile strength reduction and the microwave exposure time and the effect of microwave power level on the residual tensile strength of concrete are obtained. The experimental research shows that the tensile strength reduction of concrete induced by microwave irradiation is dependent on the concrete component, microwave exposure time, microwave power level, and cooling method after irradiation. It is expected that the findings in the paper will become the basis of the future research of concrete and rock degradation induced by microwave irradiation, and will aim in searching the new method of breaking concrete and rock more efficiently.