The adsorption layer thickness of water reducer on the cement surface was measured through the XPS spectrum and the calculating method of XPS information depth.The results showed that the adsorption layer thicknesses of lignosulfonate(LS)

modified lignosulfonate(GCL1-T)

naphthalene sulfonate formaldehyde condensate(FDN) and aminosulfonate formaldehyde condensate(ASP) on the cement surface were respectively 8.70 nm

10.87 nm

1.50 nm and 7.26 nm

while those of GCL1-T and FDN on the fly ash surface were 6.76 nm and 0.95 nm.This method could describe the adsorption layer thickness of the water reducer exactly.From the results

it could be further concluded that the electric repulsive force was the main factor of the dispersion mechanism of FDN

while the steric repulsive force could not be neglected in the dispersion mechanisms of LS

GCL1-T and ASP.