Continuing work in both laboratory and field with water-reducing and set-retarding admixtures has resulted in further helpful knowledge concerning them and has added to confidence in their use on the job. Significant benefits are obtained with these admixtures in job concrete, particularly in warm weather. Through postponement of the vibration limit, cold joints are less a hazard.
Reduction in water requirement to a large extent offsets normal increases in water due to warm weather, and due to higher slumps whatever their cause. At two days and later ages, strength is increased when the dosage is not above normal. At various ages beyond the first few days, the higher strengths achieved are greater than can be ascribed to reduction in water-cement ratio. Fear of the sugar content of the admixtures is apparently unfounded; troublesome delay in hardening is more likely to be the result of gross overdosage from malfunction of a dispenser. Hence dispensing equipment must be completely reliable and its performance readily verified for each batch. Such equipment is described.
Performance of the admixtures usually varies with concrete temperature and somewhat with various cements. Expected performance should be verified in advance using job materials. Dosages and sometimes the admixture must be changed accordingly, based on such test results and job performance.
The paper discusses these matters with related test data. It also discusses practical aspects of specifications, delivery, and acceptance testing when these are appropriate.