Volume 2, Issue 6 (June 2005)
Performance of a New Co-Polymer Sulfonate-Based Mid-Range Water-Reducing Admixture
At the present time, there are essentially two types of water-reducers: high-range water-reducers and conventional water-reducers. Superplasticizers allow a 15–30 % water reduction. They are very efficient to disperse cement particles in concretes made with W/C ratios between 0.25 and 0.45. For concrete having a W/C ratio between 0.45 and 0.60, the optimal dosage is not generally very high and lacks robustness. In industrial applications, the use of superplasticizer in 0.45–0.60 W/C ratio concrete can result in segregation (light over-dosage) or a rapid slump loss (light under-dosage).
The use of conventional water-reducers, obtained mostly from more or less processed and treated industrial by-products, results in a water reduction of between 5 and 10 %. Moreover, because they almost always contain some impurities, essentially sugars and surfactants, their dosage cannot be increased without causing excessive air entraining and a long delay in setting.
To cover the W/C ratio range between 0.45 and 0.60, it is necessary to use admixtures of the mid-range family, which are usually obtained by mixing a superplasticizer and a conventional water-reducer or a water-reducer and an accelerator. This method presents several disadvantages linked to formulation adjustment and to the availability and quality of lignosulfonate water-reducers, which may decrease in the future due to a drastic change in the production of pulp and paper worldwide.
A new type of synthetic mid-range water-reducer has been developed in order to meet the requirements of the mid-range water-reducers: comfort of rheology, no effect on setting time, and no air entrainment. It is a co-polymer of the polysulphonate family adapted for concretes made with a W/C ratio between 0.45 and 0.60. The performance of the last version of this product has been studied on grouts having a water/cement ratio of 0.45 and on concretes having a water/cement ratio of 0.44. This performance has been compared to the performance of two commercial mid-ranges and a classic water-reducer, lignosulfonate-based.
The synthetic mid-range showed a very promising dispersing performance and robustness adapted to the concrete formulation generally covered by mid-range water-reducers. Its very definite chemical composition and its controlled production make this new polysulphonate co-polymer an interesting alternative for the formulation of mid-range water-reducers.