The Influence of the Chemical Structure of Polycarboxylic Superplasticizers on their Effectiveness in Cement Pastes

The efficiency of polycarboxylic superplasticizers (derivatives of acrylic (SP-A and SP-B) or maleic (SP-C and SP-D) acids) after esterification with polyoxyethylene glycols (PEG) in cement pastes was analysed.The chemical structure of the superplasticizers was defined by gel permeation chromatography (GPC) and Fourier transformed infrared spectroscopy (FTIR). According to the experimental results the superplasticizers - derivatives of maleic acid – display greater molar mass and are built from backbone polymaleic chains and very long side polyoxyethylene chains.It is shown that acrylic superplasticizers display lower molar mass and are built from polyacrylic backbone chains and a higher number of shorter polyoxyethylene side chains. The efficiency o superplasticizers has been measured through their hydrophilicity, defined as the absorbance ratio of the ether band AET1110 (STRCH2–O–CH2ET) (referred to as the hydrophilic oxyethylene groups) to the ester band AES1730-40(STRC=OES) (referred to as the hydrophobic ester groups O=C–O–C) (with constant contents of aliphatic groups). A higher hydrophilicity of maleic superplasticizers, in comparison to acrylic, results from greater participation by the hydrophilic than the hydrophobic groups. It is shown that superplasticizers based on maleic anhydride derivatives (SP-C and SP-D) are more efficient than superplasticizers – acrylic acid derivatives (SP-A and SP-B).