The relation between porosity, microstructure and strength, and the approach to advanced cement-based materials

A theory is formulated to connect the strength of cement paste with its porosity. The theory shows that bending strength is largely dictated by the length of the largest pores, as in the Griffith (1920) model, but there is also an influence of the volume of porosity, which affects toughness through changing elastic modulus and fracture energy. Verification of this theory was achieved by observing the large pores in cement, and then relating bending strength to the measured defect length, modulus and fracture energy. The argument was proved by developing processes to remove the large pores from cement pastes, thereby raising the bending strength to 70 MPa. Further removal of colloidal pores gave a bending strength of 150 MPa and compression strength up to 300 MPa with improved toughness. Re-introduction of controlled pores into these macro-defect-free (mdf) cements allowed Feret’s law (1897) to be explained.

[1]  J. E. Bailey,et al.  On the hydration of Portland cement , 1978, Proceedings of the Royal Society of London. A. Mathematical and Physical Sciences.

[2]  J. Byrne,et al.  Stress Concentration in Concrete , 1964, Nature.

[3]  Malcolm D. Bolton,et al.  A guide to soil mechanics , 1979 .

[4]  D. Roy,et al.  Optimization of strength in cement pastes , 1975 .

[5]  K. Kendall,et al.  Flexural strength and porosity of cements , 1981, Nature.

[6]  N. McN. Alford,et al.  A theoretical argument for the existence of high strength cement pastes , 1981 .

[7]  R. Narayan Swamy,et al.  Polymer reinforcement of cement systems , 1979 .

[8]  J. H. Brown,et al.  Measuring the fracture toughness of cement paste and mortar , 1972 .

[9]  G. W. Groves.  Portland cement clinker viewed by transmission electron microscopy , 1981 .

[10]  N. Alford,et al.  An assesment of porosity and pore sizes in hardened cement pastes , 1981 .

[11]  R. Hill,et al.  Book Review: Mechanical properties of non-metallic brittle materials. Edited by W.H. WALTON. Butterworths, London; Inter-Science, New York, 1958. 492 pp., 90s , 1960 .

[12]  A. A. Griffith.  The Phenomena of Rupture and Flow in Solids , 1921 .

[13]  John R. Rice,et al.  Fracture of Brittle Solids (Cambridge Solid State Science Series) , 1975 .

[14]  C. C. Wu,et al.  Microstructural Dependence of Fracture Mechanics Parameters in Ceramics , 1978 .

[15]  A. Hellawell,et al.  The hydration of Portland cement , 1978, Proceedings of the Royal Society of London. A. Mathematical and Physical Sciences.

[16]  J. Birchall,et al.  Some general considerations of a membrane/osmosis model for portland cement hydration , 1980 .

[17]  W. Steele.  Adsorption at the Gas-Solid and Liquid-Solid Interface. , 1984 .

[18]  J. E. Bailey,et al.  Fracture measurements on cement paste , 1976 .

[19]  J. Beaudoin.  Porosity measurement of some hydrated cementitious systems by high pressure mercury intrusion-microstructural limitations , 1979 .

[20]  H. Hilsdorf,et al.  Fracture mechanics studies on concrete compounds , 1977 .