Polymer-cement matrices

Most of the developments of polymer-cement matrices for GRC were based on the use of polymer latex modified GRC. The concepts behind this approach are essential ly the same as those described for E glass In Section 8.6.1 providing improved chemical resistance, and the prevention of the growth of dense and rigid hydration products around the glass filaments. The influence of various types of polymers was evaluated at the Building Research Establishment in the UK [129-131], while the effect of an acrylic polymer latex (Forton) which was developed specifically for E-GRC (Section 8.6.1) was studied in the Netherlands with AR-GRC [101,104]. 

The different types of high performance systems will than be treated separately, based on classification in terms of the performance and the strategy to achieve it, to include the following topics monofibre systems with normal strength matrix, monofibre systems with high strength matrix, hybrid FRC, slip hardening fibres and FRC with polymer-cement matrices. 

The liquids used were 1 1 mixtures of EBA-HV and liquid methacrylate which also contained dihydroxyethyl-p-toluidine as the accelerator. Both mono- and di-methacrylates were used. The benzoyl peroxide initiator was included in the EBA zinc oxide/silanized (1 1) glass powder. These polymer cements set 5 to 10 minutes after mixing. Since there is a substantial amount of monomer in the liquid (50%) the contribution of the polymer to the strength of the cement must be considerable. Brauer Stansbury (1984b) suggested that the two matrices, the polymer matrix and the salt matrix, may be interpenetrating but separation of the two phases is likely. 

Figure 12 SimpliGed model of formation of polymer-cement co-matrix.

Abstract. The presence of water-soluble polymers affects the microstructure of polymer-modified cement mortar. Such effects are studied by means of SEM investigation. Polyvinyl alcohol-acetate (PVAA), Methylcellulose (MC) and Hydroxyethylcellulose (HEC) are applied in a 1 % polymer-cement ratio. The polymers provide an improved dispersion of the cement particles in the mixing water. The tendency of certain water-soluble polymers to retard the flocculation of the cement particles minimizes the formation of a water-rich layer around the aggregate surfaces. They also provide a more uniform distribution of unhydrated cement particles in the matrix, without significant depletion near aggregate surfaces. Both effects enable to reduce the interfacial transition zone (ITZ). The polymers also provide a more cohesive microstructure, with a reduced amount of microcracks. 

Intermingling of polymer films with the cement matrix. In the PVAA and HEC modified mortars, polymer film formation is not so easily detectable by SEM investigation. Nevertheless, it is possible that polymer films or bridges are present in the finer capillaries and intergrown within the cement matrix on a submicron scale, which makes them much more difficult to detect, but which may be even more important for the overall properties of the material. Therefore, the effect of under water storage is studied. 

Cracks can be initiated during shrinkage, mechanical testing, sample preparation or SEM analysis. Therefore, all samples were prepared and handled in the same way. It is observed that the polymer strengthens the cement matrix and increases the internal cohesion. Similar observations are made by Muller using ultrasonic auscultation technique [10]. 

The use of polymers must be accompanied by the adoption of a greater mix of energy, so that its effects are more intense and evenly distributed in the cement matrix. The analyze of concrete microstructure is a good way to assess the behavior of mechanical properties and others properties, by the visualization of formed hydrates of Portland cement and its distribution. Research into the combination of polymers with different characteristics appears to be a noteworthy path to continue. 

Polymers such as EVA, are used as admixture because it modify the elastic modulus, toughness, permeability and bond strength to various substrates in cement and mortars [10]. The polymer forms a film that creates a network inside the cement matrix, partially covering hydrated and anhydrous cement particles, sealing pores and bridging microcracks. Besides, this addition also changes the hydration rate. Silva et al [11] compare the effects of two polymers a water soluble polymer (HPMC — hydroxypropylmethylcellulose) and a latex [EVA-poly(ethylene-co-vinyl acetate)] on... 

Application of polymer modifiers, on the level of at least 5% of cement mass, results in the formation of continuous membrane that penetrate the cement matrix, in the change in shape and dimensions of crystals within the cement binder and in general reduction of composite porosity due... 

The technology of concrete impregnation with organic polymers is the most commonly known [173]. The sulphur impregnated concrete was also studied, however, the durability of this material was poor, because of the instability of sulphur in the highly basic cement matrix. 

Khazanchi AC et al (1990) Material science of natural organic fiber reinforced composites in polymer/cement/mud matrix for construction engineering. In Hamelin P, Verchery G (eds) A book on textile composites in building construction. Pluralis, France, pp 69-76... 

The investigations mentioned above, are focused principally on the processing and mechanical response of polymers reinforced with natural fibers, without considering that their mechanical properties decrease after exposition to alkaline environmental of cement materials or weather. Natural fibers reduce their mechanical properties after exposition to alkaline environment of the cement matrix, nevertheless the use of polymeric matrix as a binder aroimd the natural fibers provides protection for them. However, if the interface of composites is not good, and/or matrix is not alkaline resistant, hydration products like calcium hydroxide will migrate to interface, and polymer composite will deteriorate. Several studies have demonstrated that the mechanical properties of natural fibers decrease after exposure to alkaline environment of the cement matrix due to three different mechanisms [30-39] ... 

The dispersed polymer phase throughout the concrete causes considerable reduction in porosity and microcracks in the Portland cement matrix as well as serving as an additional binding material [11, 19]. Thus, PPCC is a more durable and weather resistant material for deck coverings and parking lot overlays. 

The particular temperatures at which peaks are observed can be used for the identification of components in a mixture, and the size of a particular peak can be used for quantitative evaluation. Examples include the determination of quartz in clays and analysis of the constituents of polymer blends, both of which would be difficult to achieve by other means. DTA has been used to determine the presence and degree of conversion of high-alumina cement concrete (HAC), a material subject to severe loss of strength under certain atmospheric conditions due to solid-state reactions in the cement matrix. Figure 9 shows a DTA curve for partially converted HAC together with the way the data are used for a conversion measurement. 

The intercalation of poly(acrylamide)-montmoriUonite superabsorbing polymer composites (SAPCs) into an aluminate cement matrix leads to a noticeable improvement in the mechanical properties of the hardened cement paste. The addition of as little as 0.6% SAPCs increases the compressive strength from 36.1 to 44.4MPa, the modulus of elashcity from 7.8 to 11.1 GPa, and the split tensile strength from 3.3 to 7.0MPa, for a W/C ratio of 0.4 (Gao et al, 1997). 

Figure 13.4 Simplified images of stnicture of a polymer cement concrete consecutive stages of formation of a polymer cement co-matrix. Reprinted from Cement and Concrete Composites, Vol 20, Ohama, Y., Polymer-based admixtures , pp. 24., Copyright (1998), with permission from Elsevier.

It is believed that a co-matrix phase which consists of cement gel and polymer films is generally formed as a binder according to a three-step simplified model shown in Fig. 2.2.Grosskurth proposed a similar model indicating the formation of the polymer-cement co-matrix.I l Sugita, et al.l l have recently investigated the microstructures and composite mechanism of latex-modified pastes and mortars, and found the interfacial layer of... 

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