Firing Resistance of Ordinary Portland Cement Pastes Incorporated a Waste of Building Bricks

Hassan Hassanien Mohamed Darweesh

doi:10.11648/j.ajche.20170506.14

Abstract

Addition of fine materials, as clay bricks or Homra (H) to Ordinary Portland cement (OPC) is evidently increases resistance to firing. Effect of firing temperature on physical, mechanical properties and phase composition of cement pastes is investigated. H can react with lime liberated from hydration of OPC. This improves morphology and microstructure of formed hydration products. OPC cement was partially substituted by 0, 5, 15, 25 and 35 wt.% H. Cement pastes were subjected to firing for 3 hours at temperatures 100, 200, 300 400, 500 and 600°C. Results showed that loss on ignition of various cement pastes increased with temperature as well as with H. Density decreased with temperature up to 400°C, while porosity increased, Above 400°C, density increased and porosity decreased. Compressive strength of OPC pastes increased with temperature up to 500°C and then decreased. Those incorporated H increased only up to 400°C and then decreased. Hardened cement pastes with 15% H recorded highest compressive strength value at 400°C while the OPC at 500°C. SEM images showed a microstructure of well-developed crystals of CSH and CAH. Ca(OH)2 are spreading in matrix at temperatures up to 400°C. There are some cracks at 600°C.

Highlights

IntroductionWhen the building materials are exposed to fire, some deterioration effects can occur
The hydrated Portland cement pastes contain a large amount of Ca(OH)2, which dehydrated to CaO between 500°C and 600°C
The water of consistency increased as the content H increased and did the setting times (Initial and final). This is essentially attributed to the nature of H which is voracious for water and it is necessary to proceed pozzolanic reactions between H and the evolved Ca(OH)2 from the hydration process [6, 7]

Summary

Introduction

When the building materials are exposed to fire, some deterioration effects can occur. This can often reach to a level at which the structure may have to be thoroughly renovated or completely replaced. Heat resistance materials are usually used for structural purposes. The need for such building materials is important in the chemical and metallurgical industries, and for the thermal shielding of nuclear power plants. The hydrated Portland cement pastes contain a large amount of Ca(OH), which dehydrated to CaO between 500°C and 600°C. The Portland cement containing 20±30 wt.% fly ash possesses a good fire resistance and dimensional stability when exposed to high temperature and high humidity or wetting [5, 6]. The replacement of OPC by 20 wt.% of thermally activated kaolinite in cement paste increases its thermal stability against temperature up to 600°C [7]

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