| Polycarboxylate based superplasticizers（PCE）,as a new generation of high-efficiency superplasticizer,has been widely used in high-performance concrete production due to its excellent water-reducing and slump-retaining ability.However,with the high-quality sand and gravel resources becoming increasingly scarce,the clay in aggregate will greatly weaken the water reducing performance of PCE and limit the use of PCE in construction.In order to improve the clay tolerance of PCEs,it is more economical and convenient to compound sacrificial agent with PCE,compared with adjusting PCE molecular structure.However,most of the current research results in this field have applied for patents,and the mechanism of the sacrificial agent is rarely reported.Therefore,this research focuses on the selection and application of sacrificial agents.In this paper,a serier of sacrificial agents have been selected from clay swelling inhibitors by the fluidity test,including Polyetheramines（D2000）,Dodecyl trimethyl ammonium bromide（DTAB）and Tetrabutyl ammonium bromide（TBAC）.The effect of sacrificial agents on the working performance of cement-montmorillonite paste has been tested.Results showed that compounding 0.12wt%of D2000,DTAB and TBAC can increase the fluidity of cement-montmorillonite paste from 197 mm to 250 mm,253 mm and 240 mm,respectively,and reduce the yield stress from 5.04 Pa to 1.12,1.08 Pa and 1.30 Pa respectively.The working mechanism of which were investigated using Thermogravimetric,X-ray diffraction and Total organic carbon analysis.Results showed that polyetheramine and alkyl quaternary ammonium sacrificial agents can diffuse to the clay surface preferentially and enter the interlayer through cation exchange with Ca2+and Na+,then occupy the adsorption sites of PEO side chain.The polyether side chain and The alkyl side chain can further prevents the chemical intercalation of PCE,which significantly improves the working performance of the cement-montmorillonite pastes.Besides,effects of sacrificial agents on the mechanical properties and durability of cement-montmorillonite mortar were investigated using compressive and flexural strength test and chloride ion unsteady state electromigration test.The results showed that sacrificial agent can obviously improve the mechanical properties and reduce migration coefficient of cement-montmorillonite mortar,especially polyetheramine D2000.Compounding 0.12wt%of D2000 can increases the 28 d and 90 d compressive strength of cement-montmorillonite mortar by 23.4%and 21.6%,respectively,and can reduce the unsteady electromigration coefficient of chloride ion at 28 d and 90 d by35%and 7.6%,respectively.This is because sacrificial agent can promote cement hydration and reduce the generation of harmful defects in the matrix by enhancing the clay tolerance of PCE,thereby reducing the porosity of mortar. |
