Influence of microstructure on properties of refractory concretes

Abstract

This dissertation is concerned with investigation of influence of microstructure on refractory concrete properties. Refractory concretes were designed on basis of following components: synthetic aggregates - corundum and bauxite, high-aluminate cement and admixtures. Main goal of the investigation is to find correlation between microstructure and the most important concrete properties such are: physical, mechanical, thermo-mechanical properties and parameters of sintering process. There is insignificant number of papers in accessible literature that are concerned with theme of effect which microstructure has on corundum and bauxite based refractory concretes. Two groups of refractory concretes were investigated: first group contained corundum as aggregate and second group contained bauxite as aggregate and chamotte as filler. Concrete design was modified with admixtures: Litopix and silica fume. Hardened concrete specimens were thermally treated at following temperatures: 110, 300, 800, 1000, 1300 and 1500oC. Afterwards, following properties were determined: bulk density, water absorption, and apparent porosity, mechanical compressive and flexural strengths. Image Pro Plus program for image analysis was applied for determination of size and number of pores within concrete structure. Non-destructive investigation method (Ultrasonic Pulse Velocity technique) was used for determination of correlation between compressive strength and temperature, and also porosity and temperature. Refractoriness and refractoriness under load were investigated for both groups of concrete. Mechanism of sintering and rate of sintering process were investigated during secondary state creep. Phase composition of refractory concretes was investigated using XRD. Micro-structural changes on following temperatures: 110, 1000 and 1500οC were followed on SEM micro-photographs. Chemical composition of grains and cement matrix was determined with EDS. Investigation results showed that both corundum and bauxite based concrete can be used as lining of metallurgical plants, as well as other plants operating at high temperature. Corundum based concretes showed better properties than bauxite concretes. Properties of both groups of concrete were improved with application of admixtures. Silica fume decreased water-cement factor, improved packing of componential grains and enabled mullite formation at 1500oC. Silica fume, also, decreased porosity and increased mechanical flexural and compressive strength of both bauxite and corundum concretes. In case of bauxite concretes, silica fume increased refractoriness and refractoriness under load. Litopix stabilized concrete structure by which degradation of mechanical properties was prevented. Corundum concrete with silica fume as admixture showed highest thermo-mechanical, mechanical and thermal properties. This dissertation represents contribution in global investigation of phenomena of micro-structural formation and its influence on properties and performances of concrete subjected to high…