Polymer-cement properties

Hornsby, P. R. (1977). A study of the formation and properties of ionic polymer cements. Thesis for PhD, Brunei University, Middlesex, England. 

Properties of Polymer Cement in Comparison with Conventional Cement... 

The properties of a latex depend on the nature of polymers in the latex, particularly the monomer ratio in copolymers and the type and amount of plasticizers. The monomer ratio affects the strengths of the latex modified mortars to the same extent as the polymer-cement ratio [87, 92]. Mechanical and chemical stability, bubbling and coalescence on drying all depend on the type and amount of surfactants and antifoamers and the size of dispersed polymer particles. It is important that the use of selected antifoamers and surfactants as stabilizers or emulsifiers produces no adverse effect on cement hydration. 

Although the mix design of latex-modified mortar and concrete is done in much the same way as that of ordinary mortar and concrete, properties such as workability, strength, extendibihty, adhesion, watertightness and chemical resistance are controlled by the polymer-cement ratio rather... 

The presence of the cement hydrate/polymer comatrix in LMM and LMC confers superior properties, such as high tensile and flexural strengths, excellent adhesion, high waterproofhess, high abrasion resistance and good chemical resistance, when compared to ordinary cement mortar and concrete. The degree of these improvements however depends on polymer type, polymer-cement ratio, water-cement ratio, air content and curing conditions. Some of the properties affected by these factors are discussed below [87, 88, 93-95]. 

The nature of the polymer latex is determined by the monomer ratio in the copolymer and this property of the latex affects strength values in manner similar to that obtained with the polymer-cement ratio. The effects of polymer-cement ratio on strength are presented in Table 6.14 [87]. 

Table 6.14 Effect of polymer-cement ratio on mortar properties (Ohama et al.)...

Latex-modified mortar and concrete mix design should recognize its improved properties such as tensile and flexural strengths, extensibility, adhesion, and durability over conventional mortar and concrete. These properties are controlled by the polymer-cement ratio rather than the water-cement ratio. Therefore, the polymer-cement ratio should be determined to meet desirable requirements. The polymer-cement ratio is defined as the weight ratio of the amount of total solids in a polymer latex to the amount of cement in a latex-modified mortar or concrete mixture. 

The polymer-cement ratio (P/C) to give the required secondary properties is determined on the basis of information shown in catalogs and technical data by the manufacturers of polymer latexes for cement modifiers. Simultaneously, the binder-void ratio (a) to satisfy the required oc and P/C is determined by using an equation for compressive strength prediction. 

Latex-modified mortar and concrete are made by using a composite binder of inorganic cements and organic polymer latexes, and have a network structure which consists of cement gels and microfilms of polymers. Consequently, the properties of the latex-modified mortar and concrete are markedly improved over conventional cement mortar and concrete. The properties of the fresh and hardened mortar and concrete are affected by a multiplicity of factors such as polymer type, polymer-cement ratio, water-cement ratio, air content, and curing conditions. 

Latex-modified mortar and concrete have a markedly improved water retention over ordinary cement mortar and concrete. The water retention is dependent on the polymer-cement ratio. The reasons for this can probably be explained in terms of the hydrophilic colloidal properties of latexes themselves and the inhibited water evaporation due to the filling and sealing effects of impermeable polymer films formed. Accordingly, a sufficient amount of water required for cement hydration is held in the mortar and concrete and, for most latex-modified systems, dry cure is preferable to wet or water cure. This is also examined in Sec. 2.1. 

Effects of Control Factors for Mix Proportions. The binder of latex-modified mortar and concrete consists of polymer latex and inorganic cement, and their strength is developed as a result of an interaction between them. The polymer-cement ratio has a more pronounced effect on the strength properties than the water-cement ratio. However, this effect depends on polymer t3rpe, air content, curing conditions, etc. The relation between the strength properties and polymer-cement ratio has been discussed in a number of papers.P l 1 1 A general trend which summarizes the results obtained in these papers is presented in Fig. 4.19. 

Avery useful aspectof latex-modified mortars and concretes is their improved adhesion or bond strength to various substrates compared to conventional mortar and concrete. The development of adhesion is attributed to the high adhesion of polymers. The adhesion is usually affected by polymer-cement ratio and the properties of substrates used. The data on adhesion often show considerable scatter, and may vary depending on the testing methods, service conditions or porosity of substrates. 

Similar to latex-modified systems, the properties of redispersible polymer powder-modified systems are improved in comparison with ordinary cement mortar and concrete, and these depend on the nature of polymer and polymer-cement ratio. Figs. 5.3 to 5.5i l represent the strengths, adhesion to cement mortar, water resistance, and water absorption of the redispersible polymer powder-modified mortars. The properties are improved with an increase in the polymer-cement ratio. This tendency is very similar to that of the latex-modified systems. In general, the redispersible polymer powder-modified mortars are inferior to SBR-modified mortar (control) in certain properties. VAA eoVa powder-modified mortars show tetter properties than EVA powder-modified mortars as seen in Fig. 5.5. The film formation characteristics of recent redispersible polymer powders for cement modifiers are improved, and continuous polymer films can be found in the redispersible polymer powder-modified systems as seen in Fig. 5.6. This contributes greatly to improvements in their properties. 

Figure 5.10 Strength properties of patching mortars using redispersible polymer powders with polymer-cement ratio of 10%. ( 1993, ASTM, reprinted with permission.)...

The mechanical properties, the corrosion stability, and some useful properties are the reasons for the continuous interest shown in polymer-concrete composites by various design, research, and production organizations. The most important types of polymer-concrete composites are polymer-impregnated concrete (PIC), polymer-cement concrete (PCC), and polymer concrete (PC). 

Hardening of cement mortars modified with water-soluble polymers comprises both cement hardening by hydration as well as polymer solidification by coagulation and film formation. Whereas the effect of polymer dispersions on the microstructure formation is frequently studied [1], only little information is available about the effect of polymer solutions. In contrast to polymer dispersions, water-soluble polymers are dissolved in the mixing water on a molecular scale and no surfactants are needed. However, the addition of small amounts of water-soluble polymers (usually below 4%) also influences the properties of the hardened material [2], This paper deals with the effect of the presence of water-soluble polymers on the microstructure. The study is made by means of SEM investigation. Polyvinyl alcohol-acetate (PVAA), Methylcellulose (MC) and Hydroxyethylcellulose (HEC) are applied in a 1 % polymer-cement ratio. This study was part of the doctoral research of E. Knapen [3],... 

There are other properties which polymer-cement protective coatings obtain thanks to the presence of polymers, but relations between the three mentioned above and the amounts of main components are the bases of the material model [1,2], for the considered coating. The relations are difficult to define as they are not linear and the properties are contradictory to each other (e.g. waterproofness and vapor permeability). Besides the presence of particular components, such as cements, mineral fillers, polymer and hydrophobic agent significantly (positively or negatively) affects each property. 

Plan of experiment. The statistical material model of polymer-cement coating was defined as the relation between components and properties [2-3]. The laboratory tests were based on the statistical planning of experiments, which was needed by economics of tests (obtaining the maximum information with minimum number of performed laboratory tests) and the fact, that the results of the laboratory tests based on the statistic planning are more predestined to statistical analysis. 

There is no possibility to present the relation of three variables at the same time that is why the graphic presentation of the model is a set of three figures - each figure presents the relation between the value of one property and two variables. The results for technical properties were surfaces with various character. Fig. 1 shows an example. This graph shows the water penetration depth for polymer-cement coating in function of coded values polymer to fillers ratio (P/F) and hydrophobic agent to Portland cement ratio (H/C). The graph character is an elliptic paraboloid. Another example is presented in Fig. 2 (water-vapor transmission rate in function of coded values X2 and xs). 

The important matter is the fact that when values of function of two variables are analyzed, the range of material variables (coded values) is narrowed to <-l, 1>. The analysis of graphs (especially in case of hyperbolic paraboloid) shows pairs of maxima and minima (or very clear tendency to the pair of extrema. Considering the mathematics - such result is correct but considering the technical properties - it is necessary to find the extremum that would be correct and rational in an engineering sense. Some of the extrema need to be rejected as they are reached with combinations of material variable values for the polymer-cement coating which are not relevant. Such result was reached in case of the flexibility index in function of coded values polymer to Portland cement ratio (P/C) and hydrophobic agent to Portland cement ratio (H/C). The shape of surface described by this relation was a hyperbolic paraboloid (refer with Fig. 5). 

The models for each property showed that the relations between the property and composition and that the relations between the properties themselves are complicated and sometimes even mutually exclusive increasing the amount of polymer increases the flexibility and waterproofness but decreases vapor permeability, increase of waterproofness by adding more fillers does not causes the increase of flexibility, the vapor permeability is not clearly disproportional to waterproofness. It was shown that some relations which had seemed to be obvious when considering the composite material such as polymer-cement coating have not worked. That is why the specific definition of the expectations is so necessary and why the desirable material properties, their importance and weights of empiric data must be defined precisely. Using elaborated material models is very helpful in designing materials. 

In the end of this chapter the polymer-cement concretes are briefly discussed. This technology is not new as well, because it was proposed by Steinbeig in 1968 [4], However, the polymer-cement concretes reveal so unique properties that they can be classified as special concrete composites [5]. 

The addition of polymer to the concrete mixture causes the significant change of concrete properties [5], However, for these concretes quite different curing conditions are required, mainly initially in water or in very humid air and then in dry air. Therefore they cannot be used in under water concreting [5]. In practice these polymer-cement concretes are cured in the same way as cement concretes and for this reason they do not attain the assumed properties [5]. 

In some cases the hardener is not used and it is taken advantage of calcium hydroxide the catalytic effect, evolved as a product of calcium silicates hydrolysis, at the initial period of alite [61]. At resin content not exceeding 20% by mass of cement the properties of polymer-cement concrete do not differ significantly from those of polymer hardened by traditional method. 

Czamecki and Lukowski [61] mention the acryl polymers added at p/c=0.1, which provide the better abrasion resistance, important for bridge pavements and industrial floors and improve the other properties typical for these polymer-cement concretes. The authors [61] mention also the epoxy-cement concrete, the only practically used composite, in which the polymer structural hardening occurs simultaneously with cement hydration [61]. 

McHugh, A.J. etal. (1996) Processing-stracture-properties interaction in polymer-cement composites, in Proceedings MAETA Workshop on High Flexural Polymer-cement Composites, Sakata, pp.59-67. 

Wang, X., Chen, G., and Wu, K. (1992) Experimental investigations and fracture properties of ordinary concrete and polymer cement concrete, in Proceedings 9th ICCC, New Delhi, Vol. 5, pp. 557-563. 

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