Key Engineering Materials Vols. 302-303

Abstract: In order to establish a mathematic model of the autogenous deformation of concrete incorporating MgO as expansive agent, we study the characteristics of it. Based on the results of testing researches and testing data, we get a mathematic model, which can clearly reveal the characteristics of autogenous deformation of concrete incorporating MgO as expansive agent. Autogenous deformation of concrete incorporating MgO as expansive agent is steady, the expansion is not infinite and there is no retrogress. Age mainly influences the basic equation of autogenous deformation. The content of MgO (or fly ash) and temperature will magnify (or reduce) the deformation.

Abstract: Tests have been done to study the compound mineral admixtures of lithium-salt industrial residue (LSR) and fly ash. The results indicate that the addition of LSR plays a significant influence on both pozzolanic activity and strength of concrete at ages of 7d, 28 d, and 60 d respectively. An optimum dosage of LSR is identified in the compound admixtures. It is of certain practical value to the study and application of the high compound admixtures content and high fly ash content concrete.

Abstract: A three-phase composite circle model is presented in this paper to assess the effect of interfacial transition zone (ITZ) on the chloride diffusion coefficient of concrete. Firstly, the distribution of circular aggregate particles was simulated in a square concrete element. Based on the simulated concrete mesostructure, the Monte Carlo algorithm was adopted to numerically evaluate the ITZ area fraction for different concrete mixes. A parametric study was then conducted to quantify the effects of the largest aggregate diameter, ITZ thickness and aggregate gradation on the ITZ area fraction. Secondly, the ITZ was modeled as a thin-wall annular plate located between a circular aggregate particle and a thick-wall cement paste annular plate. With the three-phase composite circle model, an analytical solution was derived for the chloride diffusion coefficient of concrete. Finally, the derived solution was verified by experimental results obtained from the research literature and a quantitative relationship between the thickness and chloride diffusion coefficient of ITZ was established.

Abstract: This study has investigated the controlling ASR with high quality I class fly ash. The results show that the content of fly ash is more important than the quality of fly ash for the effect on preventing ASR. The solubility of alkali in fly ash has been studied in various alkali concentration solutions. The mechanism of a low content of fly ash accelerating swell of concrete but a high content of fly ash controlling swell is discussed for controlling ASR with fly ash contained high alkali content.

Abstract: This paper discusses the sulfate resistance and frost of mass hydraulic concrete which containing fly ash, superplasticizer and a novel MgO-bearing expansive agent (HNM), at same time, the mechanisms and processes of sulfate attack on it have been proposed. Results showed that using a water/binder ratio of 0.48 in RCC containing 50 % fly ash and 8 % HNM a durability factor of over D300 can be achieved and sulfate resistance may be improved slightly.

Abstract: Aiming at influencing factors in the abominable natural environment in permafrost district of Qinghai-Tibet railway, according to different requirements on concrete’s durability performance which exerted by different climatic conditions and different environment of Qinghai-Tibet railway, the design and the construction on site of durable concrete was investigated.

Abstract: Sulphate ion and chloride ion existed in the alkaline saline soils may cause serious problems on the durability of reinforced concrete structures, while it is found that superfine mineral powder plays positive role in the precaution of the alkaline saline corrosion. A composite cement named high performance cement (H.P.C) composed of clinker, metakaolin and fly ash powder in appropriate proportions is developed with good performance in preventing concrete from alkaline saline soil corrosion. Mortar bar test and visual examination showed that the cement could effectively control AAR and sulphate ion related expansion, and the charge passed tested according to ASTM C1202 was decreased to “negligible” level for concrete with W/B ratio of 0.3, and “very low” grade for concrete with W/B ratio of 0.45 and 0.55 when the high performance cement was used. Other properties such as low hydration heat and anti-freezing properties, as well as the uniformity of the fresh concrete (with no bleeding and segregation), made it an important material in the construction of concrete structure in alkaline saline soils.

Abstract: Based on designed and manufactured test equipment of concrete early age shrinkage, the influence of shrinkage reduce agent (SRA) on early age autogenous shrinkage of concrete was researched. The test results show that early age autogenous shrinkage of concrete was reduced with SRA added and the shrinkage-reducing ratio increased with concrete strength grade heightened. SRA could also greatly reduce early age autogenous shrinkage of concrete added with pulverized ly ash or slag. Superplasticizer would increse early age autogenous shrinkage of concrete, and the shrinkage was larger than those without superplasticizer, even the SRA mixed into. Furthermore, early age curing should be enhanced for concrete with superplasticizer.