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Several techniques for measuring the porosity and pore-size distribution in hardened cement paste (HCP) have given conflicting results. This is partly because these methods require drying or pre-treatment of specimens. Small-angle neutron scattering (SANS) allows investigation of the fine-pore porosity without any such pre-treatment. Measurements using the Pluto SANS spectrometer indicate a bimodal distribution of near-spherical pores with diameters of 5 and 12 nm. The former have a well peaked size distribution and account for 1-1.5% porosity. The pores are relatively unaffected by the water-to-cement ratios investigated although drying has the effect of collapsing the structure.

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It is demonstrated both theoretically and experimentally that fracture toughness does not directly influence the Weibull modulus of ceramic bending strength for materials that obey the Griffith criterion for crack propagation. Weibull modulus remains unchanged as toughness is increased. However, toughness variations with crack length do affect the Weibull modulus. Thus materials that display R-curve behavior or Dugdale character give an increased Weibull modulus and appear more reliable.