Study On Admixtures For Early-strength Concrete System

Cement slurry additives are materials added to improve and regulate the performance of cement slurry to meet the requirements.In order to meet the construction requirements,it is necessary to add various admixtures for performance adjustment,which leads to poor compatibility between admixtures and unfriendly to the environment.Lignosulfonate is a natural,pollution-free,abundant raw material,low cost,simple use process,and good pulping performance material.It is often used as a water reducing agent for cement slurry to improve its fluidity,but it has a retarding effect.Alcohol amine admixtures can improve the compressive strength of cement slurry and promote the setting and hardening of cement slurry.This study investigated the dispersion performance of two types of lignin sulfonates in cement slurry,and selected lignin sulfonates with excellent dispersion performance as modified raw materials;The evaluation and study on the purchasing and selling relationship of five types of alcohol amine additives on the structure promoting effect of cement slurry were conducted.Through composite experiments,alcohol amine additives suitable for sodium lignosulfonate were selected to modify sodium lignosulfonate.It is hoped that the modified sodium lignosulfonate can improve the fluidity of cement slurry while achieving adjustable early strength time.The main research content includes the following aspects.(1)The properties of sodium lignosulfonate and calcium lignosulfonate in cement slurry,including thickening,rheological properties,density,and the elasticity of cement paste,were evaluated.The results show that when the dosage of lignosulfonate exceeds 1.5%,abnormal coagulation occurs during the thickening process,leading to a sudden contraction of thickening time.Therefore,the optimal dosage of lignosulfonate is 1.0%.At this dosage,the flowability of sodium lignosulfonate is 20.5 cm,with a flowability index n of 0.631 and a consistency coefficient K of 0.5435.Compared to the flowability of calcium lignosulfonate of19.5 cm,n of 0.503 and a consistency coefficient K of 1.3968,The performance of sodium lignosulfonate is superior.(2)Evaluated the thickening,rheological properties,density,and scalability of five alcohol amine admixtures,namely ethylene glycol,ethylene diamine,ethanolamine,diethanolamine,and triethanolamine,in cement slurry.The results show that ethylene glycol,ethanolamine,and ethylenediamine have certain regularity in the thickening time and fluidity of cement slurry.As the number of amino groups increases,the thickening time of cement slurry increases.When the dosage of additives reaches 1.0%,the thickening time of cement slurry reaches 112 minutes,125 minutes,and 204 minutes,respectively,while the fluidity of cement slurry decreases,reaching 15.6 cm,15.1 cm,and 14.2 cm,respectively,and there are certain differences in other properties.For ethanolamine,diethanolamine,and triethanolamine,as the number of hydroxyl groups increases,the thickening time of the cement slurry is significantly shortened,and the fluidity also decreases.When the dosage is 1.0%,the thickening time of the cement slurry is 125 minutes,25 minutes,and 12 minutes,and the fluidity is 15.1 cm,14.6 cm,and 14.1 cm,respectively.Based on the above parameters,the structure-activity relationship of alcohol amine admixtures was explored.(3)The results of compounding sodium lignosulfonate with five types of alcohol amine admixtures showed that the combination of diethanolamine and sodium lignosulfonate can reduce the thickening time of cement slurry from 123 minutes to 57 minutes,reducing it by 68 minutes,and the fluidity of cement slurry can reach 20 cm.Compared with other alcohol amine admixtures,it has wider time adjustability and better fluidity.Therefore,diethanolamine was selected to modify sodium lignosulfonate to synthesize diethanolamine modified sodium lignosulfonate.Orthogonal experiments were used to optimize the synthesis process and determine the optimal synthesis conditions.The synthesized diethanolamine modified sodium lignosulfonate under optimal conditions reduces the thickening time of cement slurry from 174 minutes to 56 minutes,and the flowability can reach 21 cm.Compared to the cement slurry with a thickening time of 123 minutes and a flowability of 19 cm when the content of sodium lignosulfonate before modification is 1.0%,the thickening time and flowability after modification have been improved to a certain extent,making it an early strength functional admixture.