Research On The Durability Of Pumice Lightweight Aggregate Concrete And Application Analysis In Complex Environment

This paper describes a study of pumice lightweight aggregate concrete that was prepared using naturally occurring pumice in Inner Mongolia. The contemplated environment in which the concrete is to be used is the irrigation area in Hetao (the Great Bend of the Yellow River), and the concrete is intended for use in canal lining as a new type of material. Different types of concrete were prepared having regard to the local environmental and climatic conditions, including ordinary pumice lightweight aggregate concrete, flyash pumice lightweight aggregate concrete, and fiber pumice lightweight aggregate concrete. The three types of lightweight aggregate concrete were investigated separately for its durability performance in different working conditions so as to reveal the destruction and degradation behavior of pumice lightweight aggregate concrete in a complex environment. To evaluate the feasibility of pumice lightweight aggregate concrete canal lining slabs, an indoor canal lining structure simulation test was performed. Finally a field test of pumice concrete canal lining was conducted in Hetao, Inner Mongolia. The scope of study and the findings are largely as below:1. The three types of concrete were submerged at half depth in corrosive solution with different concentration for an extended period and it was noted that:After an extended submerging in salt solution, concrete mass does not vary appreciably and the relative dynamic modulus of elasticity reflects sensitively the variation of concrete internal micro structure. From this, an evolution equation was formulated that includes the relative dynamic modulus of elasticity as the damage variable. A damage evolution equation was developed that relates corrosive solution concentration and corrosion time to the relative dynamic modulus of elasticity.2. The durability test that investigated the three types of concrete under the action of double and multiple factors indicated that:Concrete damage evolves quickly in a saline environment and the internal pores of damaged concrete are filled with double salts, resulting in a lower porosity. In a saline environment, flyash pumice lightweight aggregate concrete exhibits good durability whereas fiber pumice lightweight aggregate concrete develops severe damage in fiber-mortar boundary zones. Bending load accelerates concrete durability destruction, which is in direct proportion to the loading rate.3. The three types of concrete were examined using nuclear magnetic resonance (NMR) to identify their T2 map and pore structure distribution under the action of single, double, or triple factors. The outcomes suggested:T2 maps of pumice lightweight aggregate concrete generally contain 4 peaks. In the aftermath of damage and degradation, small pores evolve into big ones, thus altering concrete permeability, porosity, and bound water saturation.4. A simulation test conducted in an open system showed that the freezing-thawing damage of aerated pumice lightweight aggregate concrete is, in essence, the accumulation of freezing shrinkage and thawing swelling. Introducing flyash is useful for improving cement mortar matrix density and the density in pumice-mortar boundary zones as well, is able to reduce the average matrix surface roughness, and is effective in narrowing down the microstructure room available for concrete deformation. Introducing fiber plays a mechanical tying and binding function in concrete freezing-thawing process, so fiber pumice lightweight aggregate concrete lining slabs help mitigate canal lining slab freezing-thawing deformation or residual deformation, prolong freezing-thawing equilibrium temperature duration, and lower canal bed base soil humidity field. The conclusion is, of course, that fiber pumice lightweight aggregate concrete is preferable in lined canal works.5. It was observed in field testing of pumice lightweight aggregate concrete canal lining that a north-south alignment canal generally has a higher bed base soil temperature than a west-east alignment canal. The maximum freezing-thawing amount occurs in the top of a north-south canal or in the shady slope in the case of a west-east canal. The heat-insulation effect offered by lightweight aggregate concrete delays the heat exchange process between the base soil and the environment such that the base soil temperature varies slowly throughout the freezing season, thanks to which the base soil freezing occurs later or does not occur at all.