Key Engineering Materials Vols. 400-402

Abstract: Frothing technics with mixed polyurethane materials have been widely used in the field of civil engineering. Polyurethane has many properties, such as frothing quickly, stronger viscidity and better elasticity. Having been frothed and vulcanized, polyurethane with other hard granules can form a new kind of backfill materials which have the higher initial strength. Based on the properties of polyurethane above, the frothing technic of polyurethane materials can be applied to consolidation and backfill of concrete and roadbed structure. In this paper, on the base of the experimental research about the materials’ properties, a test simulating an actual consolidation of subsoil was processed. The stable backfill substance used as base of pavement can be formed quickly by frothing of polyurethane in the pore space of gravels. The surface of pavement can be made from gravels and some certain polyurethane. It took 2 hours to backfill the base and to make the surface. Immediately, the loading test including static and impact load was taken. The result of the test indicated that the mechanical properties of surface and base made up of polyurethane composite materials can satisfy certain standards and specifications.

Abstract: The temperature rise of concrete during hardening is intimately related to the mix proportion, among which the cement content is a major factor. However, high-strength concrete mixes are often proportioned with low water contents which leads to incomplete hydration of cement contained therein. Hence, the conventional rule of determining concrete temperature rise solely based on the cement content may not yield accurate estimations. An experimental program has been launched to investigate the coupled effects of cement and water contents on the adiabatic temperature rise of concrete. Eighteen concrete mixes were tested with a newly developed semi-adiabatic curing test method and their adiabatic temperature rise obtained by applying heat loss compensation to the test results. The results revealed that, when the water/cement ratio is lower than 0.36, both cement and water contents have effects on the adiabatic temperature rise of concrete. Prediction formula and design chart of adiabatic temperature rise, which are accurate to ±1.3°C compared with the test results, are developed. Furthermore, prediction formula of the degree of hydration of concrete is recommended.

Abstract: In this paper, freezing and thawing resistance of CA mortar was investigated and some influential factors such as the ratio between asphalt emulsion and cement (A/C), cement types, various additives were also explored. Results indicated that a gain of mass was observed for every mixture after the test; mixtures with a higher A/C performed better in terms of higher relative elastic moduli. Mixtures proportioned by partially replacing ordinary Portland cement (OPC) with sulfoalumninate cement (SAC) underperformed in freezing and thawing property. Addition of crumb rubber powder (CRP), redispersible polymer powder (RPP) and organic fiber (FR) improved the resistance of CA mortar to freezing and thawing while that of silica fume (SF) undermined it.

Abstract: Shrinkage compensating by the expansion generated by the hydration of expansive additive is one of the important measures to improve the dimensional stability of cement-based materials. Due to the slow hydration of MgO, it may cause delayed expansion in cement and thus has been used as an expansive additive to compensate thermal shrinkage at late age in mass concrete. The relationship among the microstructure, activity and expansion properties of MgO-type expansive additive (MEA) has not been clearly demonstrated, though many researches have been focused on its expansion mechanism and expansion properties. So the industrial production and application of MEA depend much on empirical methods. Three different types of MEA are produced by calcining magnesite at 900°C, 1100°C, and 1300 °Cfor 1h in an electrical furnace. The specific surface area, activity, inner pore structure, microtopography and expansion properties of the MEA have been investigated. Results show the effect of calcination temperatures on the expansion properties of MEA results from the changes in its microstructure, specific area, and thus the activity. High calcination temperature causes growth in MgO grain, decrease in specific area and surface defects of MgO, and hence the reduction of the activity value, inducing slow hydration rate and thus delayed expansion. This study will provide a platform for well understanding various activity and expansion properties of MEA produced under different temperatures.

Abstract: In this paper, the sulfate resistance properties of concrete under loading action are studied. The concrete specimens with different water/cement ratio are prepared and correlative corrosive experiments are carried out under single damage factor (SDF) and multiple damage factors (MDF), which is relative with drying and wetting cycles. Dynamic elastic modulus is taken to characteristic the sulfate resistance properties of concrete under the action of loading, drying and wetting cycles and sulfate corrosion. Results show the corrosion mechanisms of sulfate attack due to single damage factor and multiple damage factors were not all the same, and multiple damage factors could indicate the concrete structure due to sulfate attack more exactly.

Abstract: Reinforced concrete structures may be exposed to an aggressive environment. In this case combined mechanical and environmental actions may act simultaneously and their synergetic influences have to be taken into consideration. In this contribution results of tests on two different types of concrete and mortars are presented and discussed. Capillary absorption of not carbonated and carbonated concrete has been determined. The influence of mechanical load on capillary suction has been studied separately. A moderate compressive load reduces the coefficient of capillary suction, while capillary suction is enhanced by higher mechanical loads as micro-cracks are formed. Chloride diffusion has been measured by means of the diffusion cell test. The diffusion coefficient observed in carbonated concrete is roughly speaking one order of magnitude higher than the value measured on not carbonated concrete.

Abstract: The chloride ions and sulfate ions precipitating rates in surface layer of different mortars was experimentally measured. And the concept of precipitating rate of ions and corresponding equation in cementitious materials was proposed. Further, some factors affecting precipitating rate of ions were investigated. Results indicate that the precipitating rate of ions in surface layer of mortar can be expressed well by an exponential function of time variable. And the exponent in corresponding equation is about 0.42 in investigation scope, which cannot be influenced greatly by addition of mineral admixture or type of ions such as chloride ions or sulfate ions. However, the precipitating rate coefficient of ions changes remarkably with compositions of mortar or types of ions. Addition of mineral admixture can reduce the precipitating rate coefficient of ions.

Abstract: To discuss prevention of sulfate attack, especially thaumasite form of sulfate attack (TSA), sulfate resistance cement based material (SRM) were designed and prepared, and properties of which were investigated systematically. Micro-analytical techniques were introduced to identify erosion substances especially thaumasite, namely Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscope (SEM) equipped with X-ray energy dispersive spectrometer(EDS). Results show that SRM have better sulfate resistance, as well as TSA resistance, when exposed to aggressive environment with 33800 ppm mass concentration of SO42- in magnesium sulfate solution at 5°C±2°C. When immersed in magnesium sulfate solution for 40 weeks, compressive strength and tensile strength of SRM are still higher than their initial, and those of control specimen are lower by 33.7%, 36.5% compared to its initial. Surface erosion substances of SRM named S1 are ettringite and gypsum, while those of control specimen are ettringite, gypsum, thaumasite and brucite.

Abstract: Internal sulfate ions are the main cause of delayed ettringite formation, which leads to expansive damage of cement concretes. On the other hand, the exposure of cementitious systems to chloride ions causes corrosion of reinforcement bars that finally seriously shortens the service life of reinforced concrete structures. It has been found that, when concomitantly present in cementitious systems, chlorides interact with sulfate ions. Particularly, for a given concentration of sulfate ions present, low to moderate concentrations of chloride ions bring about serious deterioration of concretes due to high amount of ettringite formed, while higher contents of chlorides tend to reduce and even completely eliminate ettringite formation. The objective of the present project is to mathematically formulate the interaction between chloride and sulfate ions in cementitious materials. Such knowledge is useful for accurate consideration of the action of chlorides on concretes used in sea environments, thus predicting more precisely their service life (this being a far important step in design).

Abstract: The experiment has been carried out to study the sodium sulfate attack on carbonized concrete. The concrete specimens with strength grade of C50 were first carbonized for 28d in the carbonation box after standard curing, and then immersed into the sodium sulfate solutions of three different concentrations. When the immersed time were up to 30d, 90d, 180d, 270d and 360d, the sulfate-ion concentrations of every layer from the surface to the inside of concrete specimen were measured by the chemical titration method. Based on the test results, the sulfate-ion diffusion regularity and the reaction mechanism of carbonized concrete are analyzed. It can be concluded that the sulfate-ion diffusion regularity and the reaction mechanism of carbonized concrete is completely different from that of un-carbonized concrete, the diffusion of sulfate-ion occupies advantage in the pore water of carbonized concrete, which increases the depth of concrete specimen attacked by sulfate solution.