Katsunori Demura

Development of polymer films by the coalescence of polymer particles in powdered and aqueous polymer-modified mortars

Abstract This paper evaluates and compares the coalescence of polymer particles (continuous polymer films formation) in powdered polymer-modified mortars (PPMMs) and aqueous polymer-modified mortars (APMMs). Polymer-modified mortars (PMMs) using various redispersible polymer powders (powdered cement modifiers) and polymer dispersions (aqueous cement modifiers) were prepared by varying the polymer–cement ratio (P/C) and were tested for the characterization of polymer films using a scanning electron microscope (SEM) after curing for 28 days. It is concluded from the test results that mortar constituents of unmodified mortar (UMM) are loosely joined with each other due to the absence of polymer films, thus having a structure with comparatively lower mechanical and durability characteristics. By contrast, mortar constituents in PPMMs and APMMs are compactly joined with each other due to the presence of interweaving polymer films, thereby forming a monolithic structure with improved mechanical and durability characteristics. However, the results make obvious the poor coalescence of polymer particles or development of inferior quality polymers films in PPMMs as compared to that observed in APMMs. Moreover, PPMMs show less uniform distribution of polymer films as compared to that in APMMs. Different powdered cement modifiers have different film-forming capabilities. However, such difference is hardly recognized in aqueous cement modifiers. The polymer films in PPMMs and APMMs may acquire different structures. They may appear as mesh-like, thread-like, rugged, dense or fibrous with fine or rough surfaces. Development of coherent polymer films is not well pronounced at a P/C of 5% in PPMMs, whereas sometimes coherent polymer films are observed at a P/C of 5% in APMMs. At a P/C of 10% or more, fully developed, coherent polymer films are observed in both PPMMs and APMMs.

Behaviour of Ca(OH)2 in polymer modified mortars

This paper deals with the effect of polymer modification on the behaviour of calcium hydroxide in modified mortars. The polymer modified mortars were prepared using powdered emulsions and aqueous polymer dispersions at various polymer-cement ratios; they were then tested for air content, moulded into specimens and cured. The cured specimens were tested for compressive strength. The fine powder samples obtained from broken specimens were subjected to x-ray diffraction, differential thermal analysis and thermogravimetric analysis. From the test results, it is concluded that formation of calcium hydroxide in the polymer modified mortars is reduced possibly because of the absorption of calcium hydroxide on polymer films formed in the mortars. The extent of reduction in the quantity of calcium hydroxide depends upon the polymer-cement ratio, polymer type or both. Generally powdered poly(vinyl acetate-vinyl carboxylate), poly(ethylene-vinyl acetate) emulsions and aqueous poly(ethylene-vinyl acetate) emulsion were found to be more effective than styrene butadiene rubber latex in reducing the quantity of calcium hydroxide in the modified mortars. The cement modifiers did not cause any detrimental effect on the degree of hydration as indicated by their higher compressive strength. Estimation of the quantity of calcium hydroxide in the polymer modified mortars therefore, does not provide a proper means for predicting their degree of hydration. (TRRL)

Water retention and adhesion of powdered and aqueous polymer-modified mortars

Abstract This paper evaluates and compares the water retention in the fresh state and adhesion or bond strength in the hardened state of powdered and aqueous polymer-modified mortars. The polymer-modified mortars using various powdered and aqueous cement modifiers were prepared with different polymer-cement ratios, and tested for water retention in the fresh state and adhesion in tension in the hardened state. In conclusion, the powdered as well as aqueous polymer-modified mortars show markedly improved water retention and adhesion in tension, which increase with a rise in the polymer-cement ratio regardless of the type of cement modifiers used. The magnitude of improvement in the water retention and adhesion in tension of the powdered and aqueous polymer-modified mortars, however, depends upon the type of cement modifiers used, polymer-cement ratios or both. Moreover, the failure mode distribution of the powdered and aqueous polymer-modified mortars depends on the type of cement modifiers used, polymer-cement ratio, or both.

Pore size distribution and oxygen diffusion resistance of polymer-modified mortars

Abstract The present paper deals with the resistance of oxygen diffusion of polymer-modified mortars which are often used as low-cost promising materials for repairing work for various reinforced concrete structures. The polymer-modified mortars using three types of commercial polymer dispersions, i.e., styrene-butadiene rubber latexes, ethylene-vinyl acetate and polyacrylic ester emulsions, and tested for pore size distribution by mercury porosimetry and oxygen diffusion by a diffusion cell method. It is concluded from the test results that the oxygen diffusion resistance of the polymer-modified mortars is superior to that of unmodified mortar, and is markedly improved with an increase in the polymer-cement ratio. The use of such mortars can be recommended as effective materials for preventing the wet corrosion of reinforcing bars in the concrete structures.

Strength and elastic properties of powdered and aqueous polymer-modified mortars

Abstract The effectiveness of powdered emulsions (powdered cement modifiers) and aqueous polymer dispersions (aqueous cement modifiers) on improvements in strength and elastic properties of mortars is investigated in this paper. Polymer-modified mortars using various powdered and aqueous cement modifiers were prepared with variation in polymer-cement ratio, and tested for flexural strength, compressive strenth, tensile strength, deflection, extreme tensile fiber strain and tensile strain. It is concluded from the test results that powdered cement modifiers affect the properties of mortars similarly as the aqueous cement modifiers and the powdered polymer-modified mortars can be used in the same manner as the aqueous polymer-modified mortars for practical applications.

Morphology of Ca(OH)2 in polymer-modified mortars and effect of freezing and thawing action on its stability

Polymer-modified mortars using powdered emulsions and aqueous polymer dispersions are prepared with various polymer-cement ratios, and observed by a scanning electron microscope for the morphological characterization of Ca(OH)2. Some polymer-modified mortars are exposed under freezing-thawing conditions, and then observed by the scanning electron microscope for the same purpose. The morphology of Ca(OH)2 in the polymer-modified mortars has been established on the basis of these observations. Moreover, the effect of freezing and thawing action on various types of morphology of Ca(OH)2 crystals in the polymer-modified mortars is examined, and the relationship is pointed out between the improved crystal structure of Ca(OH)2 in the polymer-modified mortars and their higher freeze-thaw durability.

Adhesion of Polymer-Modified Mortars to Ordinary Cement Mortar by Different Test Methods

This paper deals with the adhesion or bond strength of polymer-modified mortars to ordinary cement mortar, which is tested by different methods, and the effects of polymer types and polymer-cement ratio on the adhesion. Polymer-modified mortars using a commercial styrene-butadiene rubber (SBR) latex, ethylene-vinyl acetate (EVA) emulsion and polyacrylic ester (PAE) emulsion are prepared with various polymer-cement ratios, and tested for adhesions in tension, flexure and compressive shear. Substrate used is a mortar with a ratio of cement to standard sand 1:2. The test results obtained are summarized as follows: (1) The adhesions in tension, flexure and direct compressive shear of the polymer-modified mortars increase with a raise in the polymer-cement ratio regardless of the types of polymers and specimens. (2) The adhesion in slant (indirect) compressive shear of the polymer-modified mortars reaches the maximum at a polymer-cement ratio of about 5%. (3) The failure mode distribution of the polymer-modified mortars remarkably depends on the test methods and polymer-cement ratio. (4) The adhesion test methods which can successfully reproduce service conditions in the practical applications of the polymer-modified mortars are recommended.

A note on the comparison of crack resistance of Ca(OH)2 crystals of unmodified and polymer-modified mortars in carbonated atmosphere

Abstract The purpose of this paper is to study morphologically the effects of carbonation on Ca(OH)2 crystals in unmodified mortar and polymer-modified mortars (PMMs). For this purpose, unmodified mortar and PMMs with 25 mix proportions were prepared with various polymer–cement ratios (P/C) and subjected to a nonpressurizing accelerated carbonation test (NPACT). It was concluded that Ca(OH)2 crystals formed in unmodified mortar were weak, unable to withstand stresses generated due to carbonation-related shrinkage and therefore cracked on exposure to CO2. By contrast, Ca(OH)2 crystals formed in PMMs were strong, withstood stresses generated due to carbonation-related shrinkage and did not crack on CO2 exposure.

Morphological characterization of low sulphoaluminate - type (AFm) crystals, hollow tubules and hollow crystals in polymer-modified mortars

Abstract In order to understand the structure — property relationships of cementitious systems comprehensively, studies concerning the formation of cement hydration products have been a favourite topic of the researchers. Despite this research activity, lesser attention has been paid towards the understanding of the hydration products formed in polymer-modified mortars (PMMs). PMMs are being popularly used in the world as high performance, low — cost construction materials, particularly for finishing and repairing works. To fill the gap, authors have already reported their detailed observations on the morphological characterization of calcium hydroxide and high sulphoaluminate or ettringite-type (AFt) crystals in PMMs (1,2,3,4). Apart from this, there is much to be unveiled with regard to morphological characterization of PMMs.

PROPERTIES OF POLYMER-MODIFIED MORTARS USING STYRENE-BUTYL ACRYLATE LATEXES WITH VARIOUS MONOMER RATIOS

Research on the effect of the monomer ratio of copolymer latexes such as styrene-butadiene and ethylene-vinyl acetate latexes, on the properties of polymer-modified mortars using these latexes has been published, but there is little research on such an effect as it relates to styrene-acrylic ester-modified mortars. This paper deals with the effect of the monomer ratio on the typical properties of the polymer-modified mortars with styrene-butyl acrylate latexes. The polymer modified mortars using the styrene-butyl-acrylate latexes polymerized with various styrene/butyl acrylate monomer ratios are prepared with different polymer-cement ratios, and tested for pore size distribution, flexural and compressive strengths, water absorption, and drying shrinkage. From the test results, the effects of the monomer ratio and polymer-cement ratio on their typical properties are discussed. The properties are shown to be affected to a great extent by both monomer ratio and polymer-cement ratios.