Effects Of Water-cement Ratio Research Articles

Effect of Water-Cement Ratio on Properties of Cold Joint in Self-compacting Concrete

Effect of Water-Cement Ratio on Properties of Cold Joint in Self-compacting Concrete

Magnetic Resonance Imaging and Moisture Content Profiles of Drying Concrete

The spatial distribution of moisture in concrete, along with the role this moisture plays in various modes of deterioration, is of fundamental importance to the understanding of concrete behaviour. In this paper a new magnetic resonance imaging technique is utilized for the first time to obtain drying profiles of concrete with sub-millimetre resolution. This technique permits observation of the drying mechanisms, as well as the effects of water-cement ratio and moist curing time on drying behaviour.

Effects of Water-Cement Ratio, Curing Age, Silica Fume, Polymer Admixtures, Steel Surface Treatments and Corrosion on the Bond between Concrete and Steel Reinforcing Bar

The bond between concrete and steel reinforcing bars was evaluated by electromechanical pullout testing that involved measuring the shear bond strength and contact electrical resistivity of each sample. The bond strength was increased by steel reinforcing bar surface treatment (acetone, water, ozone, or sandblasting, with ozone treatment being the most effective and acetone treatment being the least effective), adding silica fume and polymer to the concrete, an increase in the water-cement ratio of concrete (particularly from 0.45 to 0.50), and a decrease in the curing age (particularly from 14 days to 7 days). The origins of these effects are reinforcing bar cleansing for acetone treatment (accompanied by a decrease in contact resistivity), reinforcing bar surface oxide film formation for water and ozone treatments (accompanied by increases in contact resistivity), reinforcing bar surface roughening for sandblasting, polymer interface layer formation for the addition of polymer (accompanied by an increase in contact resistivity for the addition of latex, but not for the addition of methyl-cellulose), a decreased interfacial void content (accompanied by a decrease in contact resistivity) for an increase in the water-cement ratio (because of an increase in fluidity) and for a decrease in the curing age (because of a decrease in shrinkage), and an increase in the matrix modulus for the addition of silica fume. Corrosion initially caused the bond strength to increase while the contact resistivity increased, but further corrosion caused the bond strength to decrease while the contact resistivity continued to increase.

建設材料 コンクリート構造物の鉄筋腐食に関する複合要因の影響

Some kinds of reinforced concrete structures in the natural environmental condition suffered from damages due to combined causes, i.e. chloride corrosion, carbonation, alkali-aggregate reaction (AAR), and so on. In this study, it is tried to clarify the effects of these combined deteriorating causes on the steel bar corrosion and durability of concrete structures. The first objective of this study is to investigate the effects of water cement ratio, AAR and chloride content on carbonation in concrete. The second one is to make clear the microstructure of concrete affected by combined causes. The pore volume and pore size distribution of mortar were determined by a mercury penetration method. The test results are summerized as follows; (1) The carbonation rate in concrete is not affected by the chloride content. This phenomenon is proved from the results obtained by the pore distribution measurement. (2) The carbonation rate and microstructure of concrete are affected largely by water cement ratio. (3) The chloride corrsion of reinforcing steel is accelerated by the degree of carbonation.

Utilization of textile waste cuttings as building material

Textile waste cuttings are mixed with cement as binder to produce a unique kind of composite material that looks like concrete but can be cut or nailed like wood. It exhibits certain physical and mechanical properties indicating its potential for low-cost lightweight construction.The composite material is produced from a mixture of textile waste cuttings, cement and water. Textile cuttings are taken from disposed trimmings of a garments producer and a textile manufacturer. These are cut into average lengths of 2 cm. and 6 cm., and mixed with portland cement in textile-cement ratios of 1:3, 1:4, and 1:5 by weight. Water is added in amounts corresponding to water-cement ratios ranging from 0.53 to 0.85. The mix combinations produce 18 mixtures and, with 3 specimens per mixture, a total of 54 samples.Experimental blocks with dimensions of 9.5 cm. × 14.5 cm. with a thickness ranging from 1.3 to 2.0 cm. are fabricated and tested for flexure, 1.5 cm. × 5.5 cm. × 22.5 cm. blocks for tension, while cubes of 5 cm. × 5 cm. × 5 cm. are used for compression tests. Samples are cured by submersion in water for 8 days, then tested at the age of 28 to 30 days. The tests are conducted in accordance with standard ASTM procedures for testing concrete products.Test data show that the effect of water-cement ratio and fiber-cement ratio on the strength developed follows the behavior of concrete. However, unlike concrete, the samples tested for compression do not exhibit a sudden brittle fracture even beyond the failure load, indicating its high energy-absorbing capacity. Inspite of high flammability of the textile waste cuttings, the composite material shows no evidence of burning when subjected to open flame for 30 minutes.The result of the laboratory test indicate a sturdy lighter-than-concrete building material with various potential uses—for ceilings, walls, wooden board substitute, or as an economical alternative concrete block.

Effects of water-cement ratio, quantity and fineness of sand on the evolution of lime in set portland cement systems

The water-cement ratio and the quantity and fineness of sand are shown to influence the evolution of lime in set portland cement systems. Increasing the water-cement ratio from 0.30 to 0.50 caused an increase in Ca(OH) 2 content in both portland cement pastes and mortars at all ages of hydration. For the same water-cement ratios, however, the calcium hydroxide content of the mortars were found to be significantly higher than those of the pastes. With finer sand fractions and higher sand dosages, the rate of precipitation of lime in the mortars also increased. The results have been interpreted on the basis of a ‘through-solution’ mechanism of formation of CH in which after the hydrolysis of the calcium silicates C 3S and C 2S, calcium hydroxide precipitates out of solution as crystals. With respect to the mortars the sand particles are believed to act as a ‘sink’ for the CH crystals which precipitate out of the pore solution. With increasing water content the Ca 2+ and OH − ions become easily transported through the aqueous phase to the inert sand surfaces where favourable thermodynamic conditions exists for crystallization and growth of the Ca(OH) 2 crystals.

Effect of Water-Cement Ratio and Curing on Chloride Penetration into Concrete Exposed to Mediterranean Sea Climate

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Properties of polymer latex-cement composites

The effects of water-cement ratio, air content and heat curing on the properties of polymer latex-cement composites were investigated, using saran, styrene-butadiene and acrylic latexes. Load-deflection curves, modulus of rupture (M.O.R.) tensile and compressive strength, void-cement ratio (v/c) and non-evaporable water content (w n) were determined. The latex had only a small effect on w n. Strenght-v/c ratio curves were found to be dependent on polymer type and content and on defoamer type. For the same v/c ratio, all strength values increased with the increase in saran content up to 18% content by weight. With styrene-butadiene and acrylic latexes there was only increase in M.O.R., but not in tensile and compressive strength. For composites of the same workability, increase in strength values by more than a factor of two could be obtained due to the presence of polymer. Strength-polymer content curves of these composites were interpreted in terms of the strength-v/c ratio curves and on the basis of the effect of polymer latex and defoamer on the v/c ratio of the composite. In certain cases, dry heat curing at 40°C to 60°C was found to have beneficial effects on the strength of the saran composites.

The effect of water-cement ratio on the microstructure of set Portland cement

Set Portland cement consists of a ‘gel’ phase of calcium hydrosilicates with smaller amounts of crystalline and amorphous calcium hydroxide and crystalline calcium aluminate hydrate salts together with unhydrated cement clinker minerals. Electron-optical studies of single stage carbon replicas of fracture surfaces of set Portland cement pastes show that the calcium hydrosilicates formed at low water-cement ratios, e.g. 0.25, are of a fine plate-like nature with a few fibres in the pores; an increase in water-cement ratio brings about an increase in the porosity and an increase in the fibres formed in the pores. The compressive strength falls with an increase in water-cement ratio because of the increase in porosity.