Higher Water-cement Ratio Research Articles

Protection of the Transport Infrastructure from Influence of Landslides by Suspension Grouting

Construction and operation of transport infrastructure in the mountainous areas is an extremely important task. The complex structural-tectonic conditions with highly broken relief contribute to the development of modern landslide processes. Unexpected landslide activity carries a significant threat to both the road and transport infrastructure, as well as the life and health of people who use it. There are now known many different methods for protection of transport infrastructure by landslides, but the classic methods are not sufficiently effective to ensure reliable work of roads in mountainous areas and the considerable material costs involved are not justified. The reason for this is often the heterogeneity of a soil in composition and properties. A solution to this problem is to use suspension grouting to stabilize the landslide body. It was found that the injection of cement slurries with high water-cement ratio is only possible in weathered mudstone with cracks width> 10mm, with injection pressure less than 6 atm. In this case, there is a uniform filling of cracks at a distance of 1, 5-2,0 meters from the injector. When the injection pressure increase occurs the hydraulic fracturing with the output hydraulic cement slurry to the surface. Processing of dense unweathered mudstone by suspension of colloidal silica with a concentration of 29% is possible to obtain a solid array with high strength characteristics that do not change even after 10 cycles of soaking/drying.

Design and optimization of non-circular mortar nozzles using finite volume method and Taguchi method

The structure parameters of non-circular mortar nozzles for automatic wall-plastering machines are crucial in improving the performance of spraying uniformity and obtaining a larger plastering area, higher plastering quality, and efficiency. To address the non-uniformity issues of the existing mortar nozzles, we investigate the effects of a special nozzle structure on its outlet velocity uniformity by using Taguchi methods and the finite volume method. The experimental studies are conducted under various combinations of five factors: length, width, thickness, water-cement ratio, and inlet velocity, using a standard orthogonal array provided by Taguchi methods. The results reveal that the thickness, length, inlet velocity, width, and water-cement ratio are the influential factors on the outlet velocity uniformity. The interaction effects between length and thickness, length and width, and width and thickness are also significant on its outlet velocity uniformity. A higher water-cement ratio and a lower inlet velocity should be chosen as long as it meets the requirements of plastering quality and efficiency. The study of non-circular mortar nozzles provides an important reference for its systematic design in the future.

Elimination of Negative Influence of Fluidized Bed Combustion Fly Ash on Viscosity of Cement Mix

Use of fluidized bed combustion fly ash as an admixture for manufacture of cement based composite materials is not quite common now, however, there are real ways of utilizing its potential. The most important negative feature of this fly ash is its variable chemical composition, which supports formation of new forms growing within the structure with negative impact of durability of the composite material. The morphology of this type of fly ash is also not very favorable as it has negative influence on consistency. Fluidized bed combustion fly ash considerably deteriorates consistency of cement mixture, which results in higher water-cement ratio and consequently worsening of physico-mechanical and durability parameters of the whole composite. Therefore the question arises how to eliminate this negative influence on consistency without the necessity of increasing water cement ratio.

Influence of fines content on durability of slag cement concrete produced with limestone sand

The effectiveness of limestone sand fines (material finer than 0.063mm) in controlling durability performance of slag cement concrete was investigated in an experimental program. Slag cement concrete specimens incorporating limestone aggregate were produced in two water-cement ratios leading to moderate and high-level durability. Linear regression analysis was applied to evaluate the rates and significance of change in durability performance parameters of concrete at varied levels of fines content ranging between 0 and 15%. Significant relationships between performance parameters (compressive strength, water penetration resistance, chloride migration coefficient, resistivity and abrasion resistance) and fines content were found in statistical analysis depending on the water-cement ratio. Compared to low water-cement ratio concrete specimens, the contribution of the fines on durability was more prominent for the concrete mixes with high water-cement ratio. The paper also presents a case-study on durability assessment in an on-going marine infrastructure project involving Izmit Bay Crossing Suspension Bridge. The findings obtained from the field conform with the output of this research.

Estimation on the Field Application for In-Site Recycling of the Wastes Soil from Preboring

The design criteria for a structural foundation with soil cement injected precast piles (SIP) indicate that the cement milk gains a conservatively high compressive strength. In addition, a certain amount of the cement milk is lost to the surrounding soil as a result of the high water-cement ratio. Furthermore, the cost increases since the material needs to be exported to the outside of the construction site to dispose of the waste soil. This study was carried out to develop a new mixing method to replace a portion of the cement milk with site soil and a cement hardener. The applicability of this method was confirmed by examining the basic physical characteristics of the new material by on-site conducting dynamic pile loading and bond capacity tests. The test results indicate that the new filling material reduced the bleeding and reduced the loss of filling material when compared to cement milk, but the compressive strength and the results of the dynamic pile loading and bond capacity tests were lower than those obtained for cement milk. However, the new filling material satisfies the standard criterion for structure design, and the economic benefits of implementing the proposed method, including saving on the amount of cement used and reducing the costs of transporting waste soil, were confirmed.

Permeability of Clay Concretes

This paper presents an investigation on the effect of clay addition on water permeability and air permeability of concretes. Clay concrete mixes consisted of 0 to 40% clay content incorporated as cement replacement. Flow methods using triaxial cells and air permeameters were used for measuring the injected water and air flows under pressure. It was found that the higher the clay content in the mixture, the greater the permeability. At higher water-cement ratios (w/c), the paste matrix is less dense and easily allows water to ingress into concrete. But at high clay contents of 30 to 40% clay, the variation in permeability was significantly diminished among different concrete mixtures. It was confirmed that air permeability results were higher than the corresponding water permeability values when all permeability coefficients were converted to intrinsic permeability values.

Analysis of total chloride content in concrete

This research paper presents an analysis of total chloride contents in concrete. The concrete mixtures that were approved by the municipality of Riyadh city in Saudi Arabia for a main ready mix concrete plant were considered in this study. The analysis was based on an experimental investigation of chloride levels in mixing water, aggregates, and concrete. The analysis also used the maximal total chloride limits of British Standards for the concrete in conjunction with other ingredients required for the mix.The results obtained suggest that the effect of chloride content in mixing water has minimal to moderate influence upon the chloride content of concrete up to w/c equal to 0.4. It also shows that aggregate is the critical ingredient in terms of determining the presence of chloride in concrete. Critically, the limits of chloride content in any concrete mix could be violated even though the limits of chloride content still meet some standards for their content within concrete ingredients. The proportions of any mix design are also an important factor to be considered when attempting to specify the limits of chloride content of the ingredients of concrete mixtures for any type of concrete. It is vital to investigate empirically the relationship between total chloride and chloride contents in ingredients in order to precisely define the limits of chloride content in concrete mix ingredients. Mix design that has the lowest w/c ratio is preferable as far as the chloride content is concerned. Finally, water chloride content could be higher than ASTM specified limits with mix designs that have low water cement ratios and should be lower than the ASTM limits with high water cement ratios.

Statistical justification of Model B4 for drying and autogenous shrinkage of concrete and comparisons to other models

The shrinkage prediction part of Model B4 presented in the preceding paper is here statistically justified by optimal fitting of the new NU database containing 1050 test curves and by statistical compar- isons with the existing shrinkage prediction models. Rather than attempting a point-wise constitutive model for free shrinkage, Model B4 predicts the average shrinkage of cross sections of long members, which are affected by nonuniform residual stresses relaxing due to creep and microcracking. The main improvement in Model B4, which extends the 1995 Model B3 (a RILEM recommendation), is that sepa- rate formulae are given for: (1) the drying shrinkage, which represents most of the shrinkage observed in normal concretes of high water-cement ratios, and (2) for the autogenous shrinkage, which has a different physical mechanism and is important for modern high- performance concretes with admixtures, additives and low water-cement ratios. The effect of elevated temperature on the shrinkage rate is captured through an equivalent accelerated time based on activation energy. Model B4 is statistically calibrated by the new NU database of laboratory shrinkage tests through a sequential optimization procedure which isolates different physical behaviors. The new shrinkage equations are shown to match the time curves of individual shrinkage tests well, and fit the database with minimum error. Statistics of extensive compar- isons with Model B3 and with the models of various engineering societies, including those of ACI and fib, document a superior fit of the new model to the database.

Effect of superplasticizers on the early age hydration of sulfoaluminate cement

The effects of two types of superplasticizers on the properties of CSA cement pastes during early hydration were studied. The influences of two types of superplasticizers on the properties of cement pastes, including the normal consistency, setting time, fluidity, and compressive strength, were investigated by using various methods. The hydration products of the cement pastes cured for 1 day and 3 days were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that the PCE type superplasticizer retards the early age hydration while the FDN type superplasticizer accelerates the early age hydration of the CSA cement. Both types of superplasticizers have no influence on the further hydration of CSA cement, confirmed by the calorimeter tests as well. The ultrasonic pulse velocity measurements were used to probe the influence of two types of superplasticizers on the hydration of CSA cement pastes at a high water-cement ratio (0.45). The results show that the PCE type superplasticizer retards the early age hydration of the CSA cement while the FDN type superplasticizer has little influence on the early age hydration of the CSA cement.

Study on the Secondary Interface in Microstructure of the Superfine Sand Concrete

The superfine sand concrete application in our country has a history of more than half a century. Although we have a certain understanding about the superfine sand concrete, there are few studies of superfine sand concrete interface. This experiment made up different water-cement ratio superfine sand concrete, and used scanning electron microscope to observe the secondary interface structure, the product of interface C-S-H gel had been carried on by the energy spectrum analysis. Results show that the secondary interface microstructure of the low water-cement ratio concrete is denser than high water cement ratio, and also have certain effects on macroscopic compressive strength; C-S-H gel calcium silicon ratio in the secondary interface is between 1.5 and 2.1.

An integrated recycling approach for GFRP pultrusion wastes: recycling and reuse assessment into new composite materials using Fuzzy Boolean Nets

In this study, efforts were made in order to put forward an integrated recycling approach for the thermoset based glass fibre reinforced polymer (GPRP) rejects derived from the pultrusion manufacturing industry. Both the recycling process and the development of a new cost-effective end-use application for the recyclates were considered. For this purpose, i) among the several available recycling techniques for thermoset based composite materials, the most suitable one for the envisaged application was selected (mechanical recycling); and ii) an experimental work was carried out in order to assess the added-value of the obtained recyclates as aggregates and reinforcement replacements into concrete-polymer composite materials. Potential recycling solution was assessed by mechanical behaviour of resultant GFRP waste modified concrete-polymer composites with regard to unmodified materials. In the mix design process of the new GFRP waste based composite material, the recyclate content and size grade, and the effect of the incorporation of an adhesion promoter were considered as material factors and systematically tested between reasonable ranges. The optimization process of the modified formulations was supported by the Fuzzy Boolean Nets methodology, which allowed finding the best balance between material parameters that maximizes both flexural and compressive strengths of final composite. Comparing to related end-use applications of GFRP wastes in cementitious based concrete materials, the proposed solution overcome some of the problems found, namely the possible incompatibilities arisen from alkalis-silica reaction and the decrease in the mechanical properties due to high watercement ratio required to achieve the desirable workability. Obtained results were very promising towards a global cost-effective waste management solution for GFRP industrial wastes and end-of-life products that will lead to a more sustainable composite materials industry.

Effects of Recycled Aggregates on Water-Cement Ratio for Concrete

Recycled aggregate differs from primary aggregate in that it constitutes of two types of materials: the primary aggregate and the attaching cement mortar. This study was conducted in order to investigate the effects on water-cement ratio for concrete cast with recycled aggregates derived from different origins (hollow blocks & structural concrete elements) and different mixed proportions of recycled aggregate contents. The outcomes of test indicate that higher water cement ratios are required for concrete cast with recycled aggregates as compare to those cast with primary aggregates. Also there appear no obvious relationships or consistencies that can be drawn among types of recycled aggregate.

Mechanical Properties of Plastic Concrete Containing Bentonite

Plastic concrete consists of aggregates, cement, water and bentonite, mixed at a high water cement ratio, to produce a ductile material. It is used for creating an impermeable barrier (cut-off wall) for containment of contaminated sites or seepage control in highly permeable dam foundations. The effects of water to binder ratio and clay dosage on mechanical properties of plastic concrete were investigated. The results indicate that the water to binder ratio and clay dosage have great influence on the mechanical properties of plastic concrete. There is a tendency of decrease in the compressive strength, splitting tensile strength, shear strength and elastic modulus of plastic concrete with the increase of water to binder ratio and clay dosage, while, the internal friction angle of the shear specimens is increasing gradually. To improve the resistance to deformation of cut-off walls constructed with plastic concrete, the higher water to binder ratio and clay dosage can be selected to decrease the elastic modulus of plastic concrete in the practical design and applications of plastic concrete on condition that the plastic concrete has enough compressive strength, tensile strength and shear strength.

Rebar corrosion in mortars with high limestone filler content

PurposeThis research aims to study the influence of limestone filler on rebar corrosion.Design/methodology/approachMortar samples containing 35% calcareous filler and with a rebar inserted in the axis, were cast. Specimens were cured at the open air and during 28 days in lime water. After curing, they were submerged in two electrolytes (tap water and 3% NaCl) and corrosion parameters (corrosion potential and corrosion current) were monitored over time by d.c. techniques. Simultaneously, electrochemical noise measurements were carried out. After corrosion tests, rebars were pulled out by lateral compression, and their surface observed by scanning electron microscopy.FindingsIn general, carbonate additions impaired mortar protective properties, especially in the presence of chloride and changed the nature of the protective layer on rebars. The curing process did not introduce significant differences except for mortars with a high water cement ratio cured in lime water for which the beneficial effects of the simultaneous presence of carbonate and lime in the pore solution could be appreciated. The role of carbonate additions is to provide carbonate anions to passivate rebars. This passivation process caused corrosion rates not to be so high. Carbonate anions also deposited on oxide spots which were rendered passive but this process was not uniform. Certain areas on the rebar underwent intense carbonation while others showed increased corrosion rates.Originality/valueThere are not many corrosion studies about the influence of limestone filler on rebars corrosion. Particularly, this paper deals with mortars containing high percentages of carbonate additions. Results showed that the presence of this type of admixture changes the structure of the passive layer and, sometimes, may increase corrosion rates.

Behavior of Plain Concrete of a High Water-Cement Ratio after Freeze-Thaw Cycles

An experimental study of plain concrete specimens of water-cement ratio 0.55, subjected to 0, 15, 25, 40, 50 and 75 cycles of freeze-thaw was completed. The dynamic modulus of elasticity (DME), weight loss, compressive strength, tensile strength, flexural strength, cleavage strength and stress-strain relationships of plain concrete specimens suffering from freeze-thaw cycles were measured. The experimental results showed that the strength decreased as the freeze-thaw cycles were repeated. A concise mathematic formula between DME, weight loss, mechanical properties and number of freeze-thaw cycles was also established. The influences of freeze-thaw cycles on the DME, weight loss and mechanical properties were analyzed. The experimental results serve as a reference for the maintenance, design and life prediction of dams, hydraulic structures, offshore structures, concrete roads and bridges in cold regions.

Experimental Research on the Bond Strength Influenced by Mortar Corrosion

The mortar cube specimens and anchorage specimens are corroded under the sulfate solution and dry-wet cycle method is used to accelerate the corrosion process. The compressive strength of cub specimens and bond strength of anchorage specimens of different corrosion time are tested and the corresponding relationship between mortar corrosion degree and mortar anchorage strength is established。The test result shows that: the curve that strength of mortar specimens changes with corrosion time fitted with quadratic curve significantly, and the high water cement ratio is , the faster the strength loss. After mortar corrosion, the bond strength decreases with corrosion time linearly, the high water cement ration is , the low initial bond strength the specimens has, and the little bond strength loss at the same corrosion time. The changes of bond strength with coefficient of compressive corrosion resistance coefficient is approximately lineally.

Mechanical and hardening properties of accelerator on the cement concrete composites containing metallic reinforcements

Research efforts in the past have been very successful in obtaining high strength concrete using various supplementary cementitious materials in concrete; however, the restriction on adding these mineral admixtures is primarily due to delayed reactivity with the hydration product of cement and the decelerated strength gain compared to plain cement concrete. Research efforts in the past have focused on the various aspects of improving the matrix properties and make it suitable for improving the mechanical and durability properties of concrete. Matrix strengthening envisages the improved mechanical properties and accelerators improve the accelerated rate of hardening when mixed with cement. The present study is aimed at to study the influence of incorporation of accelerators and metallic reinforcements in concrete. The effect of accelerators on the compressive strength gain properties of different concrete mixes were studied for different w/c ratio, fine to aggregate ratio, cement to total ratio and metallic fibre contents. The results showed that for lower water cement ratio (0.3) and for higher f/c ratio (0.8) the strength was higher than all other concrete mixes. Similar increase in strength was noted for higher water cement ratio (0.4) at lower finer to coarse aggregate ratio. The rate of increase in strength gain was higher for lower water cement ratio at all fine to coarse aggregate ratio. Key words: Metallic reinforcements, accelerators, compressive strength, ultrasonic pulse.

Hydration kinetics process of low alkalinity sulphoaluminate cement and its thermodynamical properties

In this paper, based on the kinetic process and mechanism of cement hydration, three basic processes of low alkalinity sulphoaluminate cement hydration are characterized, including nucleation and growth interaction (NG), phase-boundary interaction (I), and diffusion interaction (D). It also studies the influence of water-cement ratio on the hydration exothermic chemical characteristics and kinetic process of low alkalinity sulphoaluminate cement. The results show that the hydration reaction of low alkalinity sulphoaluminate cement is very rapid. The lower the water-cement ratio is, the longer the thermal effect will last. The hydration kinetic process of low alkalinity sulphoaluminate cement is NG–I–D. With a higher water-cement ratio, the hydration kinetic process will transfer from the NG process into I process with a lower hydration degree. And with the water-cement ratio increasing gradually, the hydration reaction from I process to D process is also reduced.

Study on the compatibility of cement-superplasticizer system based on the amount of free solution

The changes of free solution amount, fluidity and the time-depended fluidity loss of cement paste were examined by varying the water-cement ratio and the dosages of superplasticizer. The distribution of solution and flocculation microstructure in fresh cement paste was observed with optical microscope. The change of free solution amount and its effect on the fluidity and bleeding of cement paste was studied. The results show that the adsorbed solution amount has a great influence on the compatibility of cement-superplasticizer system, including the bleeding degree, the fluidity and the time-depended fluidity loss of cement paste. Superplasticizer increases the fluidity of cement paste by destroying the flocculated cement particle structure and increasing the amount of adsorbed solution. Polycarboxylate superplasticizer shows higher ability of adsorption than naphthalene superplasticizer. Over dosage of superplasticizer is not the primary cause of bleeding. The principle reason of bleeding is the high water-cement ratio and the insufficient enhancing ability of water adsorption of superplasticizer.

Correlation Analysis of Evaluation Indexes for Freeze-Thaw Damage of Lightweight Aggregate Concrete

Freeze-thaw damage is one of the most representative damages in concrete durability. In this study, rapid freezing and thawing tests were conducted to investigate the freeze-thaw resistance and analyze the correlation of the evaluation indexes of lightweight aggregate concrete with different water-cement ratios. The high correlation was confirmed between the length change and relative dynamic modulus of elasticity of lightweight aggregate concrete. The relative dynamic modulus of elasticity decreased with the increase of concrete length. However, the correlation was different according to the water-cement ratio values of lightweight aggregate concrete. The higher water-cement ratios, the lower expansion values of lightweight aggregate concrete when the relative dynamic modulus of elasticity decreased to the same degree under freezing and thawing action.