Lignosulfonates water reduction

Method of addition of retarder (0.225% calcium lignosulfonate by wt cement) Water-cement ratio Slump Water reduction (mm) (%)... 

The recorded data on lignosulfonate water-reducing agents indicate that, as far as freeze-thaw durability is concerned, because of the low water-cement ratios possible, an enhancement to the durability will invariably be obtained. When the admixtures are used to effect a reduction in the cement content, there are strong indications that a considerable enhancement of durability is obtained, presumably due to a reduction in the cement matrix which is the part of the concrete susceptible to frost damage. The higher aggregate content would therefore allow easier dissipation of stresses. 

Many concrete producers use a combination of superplasticizer and a conventional water-reducing, set-modifying or air-entraining admixture to achieve the desired performance. The superplasticizer provides the major portion of the required water reduction and the conventional admixture is added to achieve one or more of the following objectives (1) further water reduction (2) admixture economy (3) the desired air content (4) increased workability and (5) extension of set and workability. Coimnercial conventional admixture formulations used for this purpose are usually based on sodium lignosulfonates, hydroxycarboxylic acids or processed carbohydrates. Such combinations, besides reducing the dosage of the... 

Retardation/water reduction Lignosulfonates, corn starch syrup... 

Water reduction Salts of sulfonated naphthalene and melamine formaldehyde condensates, lignosulfonates... 

A partial explanation of the water reduction by lignosulfonate admixture is its ability to entrain air. It is reported that lignosulfonate promotes higher water reduction than hydroxycarboxylic acid-based admixtures. 

At equal dosages, all water reducers are effective in producing concrete of equal or higher compressive strength than that of reference concrete. At equal cement content, air content, and slump, the water reducers increase the 28 day strength by about 10-20%. Table 9 shows the influence of lignosulfonate type admixture on the compressive strength of concrete.Water reduction varies between 5 and 8%. 

Table 2. Water Reduction and Setting Characteristics of Mortar Containing Lignosulfonates...

Fig. 1.33 Reductions in water-cement ratio as a function of aggregate-cement ratio for lignosulfonate and hydroxycarboxylic-acid-based water-reducing agents.

For concrete used in dam construction, the results shown in Table 1.23 [99] have been obtained. From these results, it will be seen that a reduction in the water-cement ratios was obtained and in the large majority of cases (80% of the specimens) an improvement in freeze-thaw resistance was obtained. In fact, the average resistance of admixture-containing concrete was 39% greater than the control specimens. The ability of the lignosulfonates to... 

Similar data have been obtained for other lignosulfonate-based water-reducing admixtures where cement and workability were kept constant with a reduction in the water-cement ratio and the reinforcement bond was measured by ASTM C234 91a, with the result shown in Table 1.29 [107]. 

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