It is known that water-reducing chemical admixtures reduce the amount of water used for plasticizing concrete mixes such that the concrete requires less water to reach a given slump as compared to untreated concrete. A lower water-to-cement ratio (w/c) can lead to higher strength concrete without increasing the cement amount.
It is also known that polycarboxylate (“PC”) type cement dispersants are popularly used for high range water reduction (“HRWR”) applications in which water content is reduced by 12-30 percent compared to concrete that is untreated. HRWR plasticizers are referred to as “superplasticizers” and allow concrete to be highly fluid and to be placed quickly at the job site with little or no compaction effort.
For example, U.S. Pat. No. 6,187,841 of Tanaka et al. disclosed PC copolymers which functioned as HRWR dispersants and which were made from (alkoxy)polyalkylene glycol mono(meth)acrylic ester type monomers and (meth)acrylic acid type monomers, and they emphasized that large molecular sizes were required in order for the HRWR dispersant to achieve ideal water reduction capabilities.
In another example, EP 0 850 894 B1 of Hirata et al. disclosed PC copolymers which functioned as HRWR dispersants and which were made from polyalkylene glycol ether-based monomers and maleic acid based monomers. Similar to Tanaka et al., Hirata et al. disclosed molecular size ranges extending upwards to 100,000 and expressed a strong preference for using a large number of alkylene oxide groups.
In US Patent Application Publications US 2011/0166261 A1 and US 2012/0046392 A9, Lorenz et al. disclosed a PC copolymer comprising four components of an unsaturated dicarboxylic acid, an unsaturated alkenyl ether having 1 to 25 oxyalkylene units, an unsaturated alkenyl ether having 26 to 300 oxyalkylene units, and an unsaturated monomer comprising a hydrolysable moiety. This reference indicates that the copolymer demonstrated a lower binding affinity with cement particles initially and could be overdosed into the cementitious composition initially to obtain workability. Over time, the hydrolysable moieties become saponified, resulting the retention of the workability in the cementitious composition.
It is the belief of the present inventor that for low-to-mid range applications, wherein it may not be necessary or desirable to replace a large amount of water in certain concrete or mortar mixes, that the PC copolymers taught in the above prior art references do not confer sufficient initial workability to the concrete or mortar mixes.
It seems that most of the prior art in the field of PC copolymers for cement dispersant applications are intended for HRWR purposes wherein a large water cut is achieved such that the cementitious compositions have low water-to-cement ratios. As another example, in Japan Laid Open JP 2001/302305, Yamashita et al. disclosed a PC copolymer comprising an alkenyl ether having 1 to 100 oxyalkylene groups, an alkenyl ether having 11 to 300 oxyalkylene groups, and an unsaturated carboxylic acid. Again, one reads that Yamashita et al. expressly preferred superplasticizing (i.e., HRWR) applications wherein a very large water cut is achieved in the cementitious composition; and, indeed, one can see in the examples that this reference teaches very low water-to-cement ratios (e.g., 0.25-0.30 w/c) which would be much lower compared to low-to-mid-range water reduction applications.
In contrast to the extensive polycarboxylate polymer size and weight ranges taught in these exemplary art references, the present inventor believes that PC copolymers have not been sufficiently explored for low-to-mid-range plasticization, because the concrete industry has become accustomed to using the more expensive polycarboxylate (PC) type copolymers for HRWR applications, while using non-PC cement dispersants, such as lignin type plasticizers, primarily for low-to-mid-range applications. It appears that in the concrete industry, therefore, PC type copolymers are reserved customarily for high range water reduction (HRWR) applications, i.e., for achieving the 12 to 30 percent reduction in hydration water.
The present inventor has recently attempted to buck this trend. For example, in US Publication No. 2016/0090323 (owned by the common assignee hereof), Kuo et al. disclosed a method for achieving low-to-mid-range water reduction in hydratable cementitious compositions having a water/cement ratio of 0.40-0.80, wherein the method involves using one or more PC copolymers made from a polyoxyalkylene monomer, an unsaturated carboxylic acid monomer, and, optionally, an unsaturated water-soluble hydrophilic monomer.
It is an objective of the present invention to provide an alternative to lignin type water reducers and to provide an alternative low-range and mid-range water reduction approach to Kuo et al. in US Publication No. 2016/0090323, by using a polycarboxylate comb-type that achieves admixture dosage efficiency at lower water cuts (i.e., below 12 percent water cut) as compared to lignin type water reducers and conventional (e.g., larger, commercial-scale) polycarboxylate type polymers that are typically used for high range water reduction (HRWR) applications.