Abstract
Over the vast Northwest China, arid desert contains high concentrations of sulfate, chloride, and other chemicals in the ground water, which poses serious challenges to infrastructure construction that routinely utilizes portland cement concrete. Rapid industrialization in the region has been generating huge amounts of mineral admixtures, such as fly ash and slags from energy and metallurgical industries. These industrial by-products would turn into waste materials if not utilized in time. The present study evaluated the suitability of utilizing local mineral admixtures in significant quantities for producing quality concrete mixtures that can withstand the harsh chemical environment without compromising the essential mechanical properties. Comprehensive chemical, mechanical, and durability tests were conducted in the laboratory to characterize the properties of the local cementitious mineral admixtures, cement mortar and portland cement concrete mixtures containing these admixtures. The results from this study indicated that the sulfate resistance of concrete was effectively improved by adding local class F fly ash and slag, or by applying sulfate resistance cement to the mixtures. It is noteworthy that concrete containing local mineral admixtures exhibited much lower permeability (in terms of chloride ion penetration) than ordinary portland cement concrete while retaining the same mechanical properties; whereas concrete mixtures made with sulfate resistance cement had significantly reduced strength and much increased chloride penetration comparing to the other mixtures. Hence, the use of local mineral admixtures in Northwest China in concrete mixtures would be beneficial to the performance of concrete, as well as to the protection of environment.
Highlights
The 28-day and 60-day results showed that cement mortars with fly ash or slag maintained same strength level as ordinary cement mortar, which could be attributed to the fact that replacing cement with fly ash can extend the process of hydration and allow higher strength development in the long term
The present study investigated the chemical, mechanical, and durability properties of concrete made with local mineral admixtures and subjected to typical severe sulfate environment in Northwest China
SiO2 and lower Al2O3 contents than ordinary portland cement or the selected sulfate resisting cement (SRC), which would potentially improve the sulfate resistance of concrete by reducing permeability and reactive aluminates
Summary
The Northwest China, including Xinjiang, Gansu, Qinhai, partial Tibet, and partial Inner Mongolia, spans over 3.5 million square kilometers. Taking Xinjiang Urgur Automatous Region (a key province in Northwest China) as an example, in 2012, the automatous region produced 9 million kilowatt-hour of electricity from coal power plants and 2.4 million tons of steel, generating a huge amount of by-products including fly ash, silica fume and blast furnace slag. These mineral admixtures, if not utilized in time, would turn into waste materials and poses serious threat to the environment. Economic and environmental benefit of utilizing these local mineral admixtures in concrete would be tremendous
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