Abstract: This paper summarizes the principal theory of small-angle scattering technique (SAS), including Guinier approximation, Porod approximation and function of the two approximations. Application of SAS in nano-CSH particle diameter, fractal structure of nano-CSH and pore structure distribution in hardened cement pastes is also described in the paper. Advantage of the technique is nondestructive, noninvasive, and could be used repeatedly in the real-time characterization of the microstructure and its evolution. SAS, especially small-angle neutron scattering technique (SANS), also has its limit because effective neutron source is difficult to obtain, analysis of test model is too simplistic far from real fact, and experiment is costly and non-portable.

Key words: hardened cement paste%SAS%microstructure%nano CSH particle%fractal