Showing papers on "Mortar published in 2009"

Water permeability of engineered cementitious composites

Abstract: The water permeability of a unique class of high performance fiber reinforced cementitious composites (HPFRCC) called engineered cementitious composites (ECC) is investigated. These composites are deliberately tailored using microcmechanical design principles to exhibit pseudo-strain-hardening characteristics in uniaxial tension, up to greater than 4% strain. While undergoing tensile deformation, microcracks are designed to saturate the specimen rather than localize into large cracks. This tendency to form microcracks, which are experimentally shown to be approximately 60 μm in width, allows ECC material in the cracked state to maintain water permeability similar to that of uncracked concrete or mortar, and magnitudes lower than cracked reinforced mortar or concrete. It is also shown that the self-healing properties of cracks within ECC material significantly aids in reducing the coefficient of permeability of cracked ECC.

New Mixture Proportioning Method for Concrete Made with Coarse Recycled Concrete Aggregate

Abstract: New method of mixture proportioning is proposed for concrete made with coarse recycled concrete aggregates (RCA). The proposed method, dubbed the "equivalent mortar volume" method, is predicated on the fact that RCA is a two-phase material comprising mortar and natural aggregate; therefore, when proportioning a concrete mixture involving RCA, one must account for the quantity and quality of each phase and adjust both the coarse aggregate and fresh paste content of the mix accordingly to achieve the same total mortar volume as a companion mix with the same specified properties but made entirely with coarse natural aggregates of similar properties to the coarse natural aggregate contained in RCA. Using the proposed method and the conventional aggregate replacement method, a large number of mixes was made with RCA obtained from two demolition waste recycling plants. For each mix, its slump, fresh and hardened densities, compressive strength, and elastic moduli were measured. The results showed that using the proposed method, unlike the conventional method, yields concrete mixes with consistent, predictable, and comparable properties to those of similar mixes made with natural aggregates.

Durability of recycled aggregate concrete designed with equivalent mortar volume method

Abstract: Results of a comprehensive investigation about the durability of structural-grade concrete made with recycled concrete aggregate (RCA) are presented. The RCA-concrete mixes were proportioned using a new concrete mix design method, termed the equivalent mortar volume (EMV) method. The EMV method is based on the hypothesis that RCA is a composite material comprising mortar and natural aggregate; therefore, when proportioning a concrete mixture containing RCA, one must account for the relative amount and properties of each the two components and adjust both the fresh coarse aggregate and fresh paste content of the mix accordingly. Tests were conducted to study the freeze–thaw, chloride penetration and carbonation resistances of the mixes proportioned by the EMV method and by the conventional method. Results of the test showed that RCA-concrete mixes proportioned by the EMV method have higher resistance to freeze–thaw action, chloride penetration and carbonation than those designed with the conventional method, and they satisfy the current requirements for concrete exposed to severe environments.

Effect of grinding on chemical and physical properties of rice husk ash

Abstract: The effect of grinding on the chemical and physical properties of rice husk ash was studied. Four rice husk ashes with different finenesses, i.e. coarse original rice husk ash (RHA0), RHA1, RHA2, and RHA3 were used for the study. Ordinary Portland cement (OPC) was partially replaced with rice husk ash at 20% by weight of binder. The water to binder ratio (W/B) of the mortar was maintained at 110%±5% with flow table test. Specific gravity, fineness, chemical properties, compressive strength, and porosity test of mortars were determined. The differences in chemical composition of the rice husk ashes with different finenesses from the same batch are small. The use of RHA3 produces the mortars with good strength and low porosity. The strength of the mortar improves with partial replacement of RHA3 in comparison with normal coarse rice husk ash. The use of RHA3 results in a strong and dense mortar, which is due to the better dispersion and filling effect, as well as an increase in the pozzolanic reaction.

Microbial activity on the microstructure of bacteria modified mortar

Abstract: Microbial modified mortar or concrete has become an important area of research for high-performance construction materials. This study investigates the effects of incorporating a facultative anaerobic hot spring bacterium on the microstructure of a cement–sand mortar. Environmental scanning electron microscopic (ESEM) views and image analysis (IA) of the bacteria modified mortar (thin-section) showed significant textural differences with respect to the control (without bacteria) samples. X-ray diffraction (XRD) study confirmed the formation of new phases of silicates (Gehlenite) within the matrix of such mortar material, which causes an improvement in the strength of the material. Electron probe microstructure analysis (EPMA) suggested that the bacterial treatment promoted uniform distribution of silicate phases and increased the calcium/silicon ratio within CSH gel of the matrices. The bacterium is found to leach a novel protein, which is capable of isolating silica from its source. The addition of such isolated protein, instead of the bacteria, into mortar also improves the strength of mortar.

An investigation of the mechanisms for strength gain or loss of geopolymer mortar after exposure to elevated temperature

Abstract: When fly ash-based geopolymer mortars were exposed to a temperature of 800 °C, it was found that the strength after the exposure sometimes decreased, but at other times increased. This paper shows that ductility of the mortars has a major correlation to this strength gain/loss behaviour. Specimens prepared with two different fly ashes, with strengths ranging from 5 to 60 MPa, were investigated. Results indicate that the strength losses decrease with increasing ductility, with even strength gains at high levels of ductility. This correlation is attributed to the fact that mortars with high ductility have high capacity to accommodate thermal incompatibilities. It is believed that the two opposing processes occur in mortars: (1) further geopolymerisation and/or sintering at elevated temperatures leading to strength gain; (2) the damage to the mortar because of thermal incompatibility arising from non-uniform temperature distribution. The strength gain or loss occurs depending on the dominant process.

Improvement of chloride ion penetration resistance in cement mortars modified with rubber from worn automobile tires

Abstract: Disposal of worn tires poses a major problem worldwide. In Greece more than 50,000 tons of worn automobile tires are stockpiled annually. This paper presents the results of laboratory research that examines the incorporation of tire rubber granules as a partial replacement for the sand in cement mortars. Physical and mechanical properties of these rubber mixtures are studied while, for the first time, resistance to chloride ion penetration is measured. Results showed a decrease in mechanical properties, whereas an increase in chloride ion penetration resistance has been observed. This implies that cement-based mortar and concrete products, modified with tire rubber granules as a partial replacement for the sand, can be used in applications where mechanical properties are not of prime importance but where high resistance to chloride ion penetration is demanded.

Influences of fly ash on magnesium oxychloride mortar

Abstract: The application of magnesia-based construction materials draws much research interests nowadays due to the ever increasing awareness of environmental protection. By incorporation of fly ash into magnesium oxychloride (MOC) cement, an energy efficient and environmentally friendly repair material can be formed for successful industrial applications. In the current research, an appropriate formulation of the MOC matrix with a suitable combination of the molar ratios MgO/MgCl2 and H2O/MgCl2 has been characterized by using phase diagram, X-ray diffractograms and scanning electronic microscope. Subsequently the influences of fly ash on the properties of both MOC cement and mortar are investigated. It is found that the incorporation of fly ash can enhance the workability or fluidity, retard the setting time, and improve the water resistance of the MOC mortars. With the enhanced performance and a slightly expansive nature, the MOC mortars incorporated with fly ash has a good potential to be used as a repairing material.

A nonlinear homogenization procedure for periodic masonry

Abstract: The present paper deals with the problem of the determination of the in-plane behavior of masonry material. The masonry is considered as a composite material composed by a regular distribution of blocks connected by horizontal and vertical mortar joints. The overall constitutive relationships of the regular masonry are derived by a rational micromechanical and homogenization procedure. Linear elastic constitutive relationship is considered for the blocks, while a new special nonlinear constitutive law is proposed for the mortar joints. In particular, a mortar constitutive law, which accounts for the coupling of the damage and friction phenomena occurring during the loading history, is proposed; the developed model is based on an original micromechanical analysis of the damage process of the mortar joint. Then, an effective nonlinear homogenization procedure, representing the main novelty of the paper, is proposed; it is based on the transformation field analysis, using the technique of the superposition of the effects and the finite element method. The presented methodology is implemented in a numerical code. Finally, numerical applications are performed in order to assess the performances of the proposed procedure in reproducing the mechanical behavior of masonry material.

Premixing mortar with high moisture retention and production method thereof

Abstract: The invention discloses pre-stirring mortar with high moisture retention and a production method thereof. The premixing mortar comprises the following components by weight ratio: 100 parts of cement with the high moisture retention, 1 to 900 parts of fine aggregate and 30 to 200 parts of water, wherein the cement with the high moisture retention contains a cellulose ether component and has the moisture retention above 90 percent; and the fine aggregate is natural sand or artificial sand obtain through screen sizing or removing harmful components, and has the maximum grain diameter of 1.18 mm to 2.36 mm. The production method comprises the following steps: arranging a mortar stirring machine on a construction site or nearby; adopting the cement with the high moisture retention and the fine aggregate to automatically meter and stir, enable mortar to be usable while stirring, and the like to ensure the mortar quality; and adopting a closed stirring mode, a dust-collecting mode and the like to reduce dust raise. The pre-stirring mortar can effectively improve and ensure the qualities of the mortar buildings, obviously improves the construction environment, greatly decreases the production cost of the pre-stirring mortar and solves the difficult problems that the prior pre-stirring mortar has over-high cost and are difficult to popularize and apply.

Brick and Mortar Strategy for the Formation of Highly Crystalline Mesoporous Titania Films from Nanocrystalline Building Blocks

Abstract: We present a novel “brick and mortar” strategy for creating highly efficient transparent TiO2 coatings for photocatalytic and photovoltaic applications. Our approach is based on the fusion of preformed titania nanocrystalline “bricks” through surfactant-templated sol−gel titania “mortar”, which acts as a structure-directing matrix and as a chemical glue. The similar chemical composition of both bricks and mortar leads to a striking synergy in the interaction of crystalline and amorphous components, such that crystallization is enhanced upon thermal treatment and highly porous and highly crystalline structures are formed at very mild conditions. Coatings with a broad variety of periodic mesostructures and thicknesses ranging from few nanometers to several micrometers are accessible using the same organic template, and the final structures are tunable by varying the fraction of the “bricks”. The beneficial combination of crystallinity and porosity leads to greatly enhanced activity of the films in photocatalytic processes, such as the photooxidation of NO. Acting as the active layers in dye-sensitized solar cells, films of only 2.7 μm in thickness exhibit a conversion efficiency of 6.0%.