Abstract: The performances of sulfonated wheat straw lignin (SWSL), which is a sulfonated product of wheat straw lignin extracted from alkali pulping, used as concrete water-reducer were studied. When the dosage is 0.25% (based on concrete), the water-reducing ratio of SWSL reaches 13.5% which is higher than that of calcium lignosulfonate (CLS) obtained from sulphite pulping; but the 3 and 7d compressive strengths of concrete are only 113% and 105% respectively, which are lower than those of CLS. Further researches indicate that, in the alkali solution of cement paste, SWSL has good foaming property and foam stability, which result in high water-reducing ratio. However the foam of SWSL solution is large and non-homogeneous, with the largest bubble diameter of 2mm, which leads to decrease of the density of hardened mortar blended with SWSL. The content of pores with a diameter less than 0.01mm was relatively low; while the content of pores with a diameter between 0.01-0.05mm was high. Thus the compressive strength of hardened concrete was reduced. The sulfonation degree of SWSL is 1.1mmol/g and its molecular weight is 4424 only, which are all lower than those of CLS. The relatively low sulfonation degree is the reason that the dispersibility of SWSL is not comparable with CLS.

Key words: lignin, sulfonation, concrete, water-reducer