Pore Structure Characterization And Gas Permeability Of Cement-based Materials Containing High Volume Of GGBS

Cement-based materials containing high volume of GGBS are widely used incivil engineering, and the durability of materials is valued. Durability ofcement-based materials depends on the pore structure and the permeability isone of the main indicators to characterizethe durability performance.Thusit isimportant to study the pore structure and peameability of cement-basedmaterials containing high volume of GGBS.To this purpose, cement pastes and mortar specimens with different w/bratios (0.3,0.4and0.5) and different GGBS contents were prepared.The porestructure of materials was characterized by mercury intrusion porosimetry(MIP) method. As the curing conditionson site are different from laborotory,the influence of curing conditionson pore structure is also investigated. Gaspermeability tests with an improved CEMBUREAU method were carried outfor mortar and concrete materials of two w/b ratios and two slag contents.Furthermore,the gas permeability of mortars and concretesat different watercontents was measured to study the influence of pore water content on the gaspermeability, and the slected degrees of water saturation are80%,60%,40%,20%and0%.The results show that incorporating GGBS into binderdecreases poresportion of size≥10nm and increases pore portion<10nm, the total porosity andspecific surface area(SSA) are increased, and the average pore size isdecreased.This phenomenon becomes more obvious as w/b ratio increases.Two peaks of pore size distribution are present in the pore size ranges of10–100nm and100–1000nmfor sealed-curing samples, and the self-desiccatoncaused by sealed-curing augments the porosity and tortuosity of pore structure,but not SSA. Too high mold or excessive vibration can lead to the segregationof concrete in specimen, resulting in the different values of gas permeabilitybetween the upper and lower parts of the specimen. Mortars and concreteshave very different gas permeability, and the gas permeability KVof mortarsshows linear relationship with φD2, where φ is porosity and D is average porediameter. The gas permeability KVreduces to zeroas the porosity is below acertain value. The relationship between relative gas permeability Krand water saturation Swtends to be observe Kr=(1-Sw)η(1-Sw1/m)2mwith differentparameters fitted for different materials.On the basis of the above research, a pretreatment procedure is proposed todetermine the gas permeability of concrete used in high integrity containers(HIC).