Cement Factor Research Articles

The Influence of Compression Applied during Production to the Compression Strength of Dry Concrete: An Experimental Study

Dry concrete is a cementitious material, consisting of aggregates imbedded in a cement matrix. The water cement factor is customary kept low, the compression stress is given to reduce the air voids in the mixture, to enable the entrapped water to optimize the hydration process, and to create more dense material so it will provide a better performance. This study uses 2 types of mix designs and 9 types of compressive stress. The experimental test showed that the greater compressive stress given during the production process increase the compressive strength of the dry concrete until it reaches the optimum point.

Effects of shrinkage reducing admixture and wollastonite microfiber on early-age behavior of ultra-high performance concrete

In this study, the effect of incorporating shrinkage reducing admixtures (SRA) and/or wollastonite microfibers on the early-age shrinkage behavior and cracking potential of ultra-high performance concrete (UHPC) was explored. Wollastonite microfibers were added at rates of 0%, 4% and 12% as partial volume replacement for cement, while SRA was added at 1% and 2% by cement weight. Results show that the reinforcing effect induced by wollastonite microfibers mitigated the reduction in compressive strength induced by SRA. Addition of wollastonite microfibers to SRA mixtures did not impart a significant change in the measured free shrinkage strain, while it enhanced the cracking resistance compared to that of mixtures incorporating SRA alone. Moreover, adding wollastonite microfibers reduced the leaching of SRA from concrete under submerged conditions, thus leading to higher efficiency of SRA in reducing shrinkage. Partially replacing cement with natural wollastonite microfibers also leads to a reduction in the cement factor, which represents economic and environmental benefits.

Research of Performance of Low Amount of Cement Manufactured-Sand Concrete

Compared with natural sand, manufactured-sand is of small porosity, poor grain shape and graded, which impacts mixes workability and the properties after hardening. In Concrete, playing the role of retaining moisture water is mainly powder, including cement, powder in the sand and fly ash etc. The amount of powder has a great influence on the properties of concrete, especially on its workability. This paper mainly discusses the influence of amount of cement, cementitious materials, fly ash, water-cement ratio and other factors on the workability, compressive strength and shrinkage of concrete. The experiments show that, in the case of the low amount of cement, workability of the manufactured-sand concrete mixture, compressive strength and shrinkage deformation of test block all meet the actual requirements.

Effect of nano-calcium carbonate on early-age properties of ultra-high-performance concrete

In this study, the effects of nano-calcium carbonate (CaCO3) addition on the early-age properties of ultra-high-performance concrete cured at simulated cold and normal field conditions were investigated. The nano-CaCO3was added at rates of 0, 2·5, 5, 10 and 15% as a partial volume replacement for cement. Similar mixtures incorporating chloride- and non-chloride-based accelerating admixtures were also tested for comparison. Results indicate the high potential of nano-CaCO3to accelerate the setting and hardening process of ultra-high-performance concrete through providing nucleation sites, increasing contact points and increasing the effective water-to-cement ratio. Although nano-CaCO3exhibited a comparable or slightly lower accelerating effect to that of the chloride- and non-chloride-based accelerating admixtures, it brings a number of benefits to concrete production. These include the development of low-maintenance structures through eliminating the risk of steel corrosion induced by chloride-based accelerating admixtures, as well as a more environmentally friendly concrete through reducing the cement factor of ultra-high-performance concrete.

Effects of nano- and micro-limestone addition on early-age properties of ultra-high-performance concrete

In this study, the effects of micro- and nano-CaCO3 addition on the early-age properties of ultra-high-performance concrete (UHPC) cured at simulated cold and normal field conditions were investigated. The micro-CaCO3 was added at rates of 0, 2.5, 5, 10 and 15 %, while the nano-CaCO3 was added at rates of 0, 2.5, and 5 %, both as partial volume replacement for cement. Results indicate that micro-CaCO3 acted mainly as an inert filler, creating a denser microstructure and increasing the effective w/c ratio. In addition, nano-CaCO3 accelerated the cement hydration process through nucleation, and also acted as an effective filling material. Mixtures combining both micro- and nano-CaCO3 resulted in similar or enhanced mechanical properties compared to that of the control, while achieving cement replacement levels up to 20 %. Thus, through the use of micro- and nano-CaCO3, more environmentally friendly UHPC can be produced by reducing its cement factor, while achieving enhanced engineering properties.

Stress-strain behavior of plastic concrete using monotonic triaxial compression tests

The mechanical behavior of plastic concrete used in the cut-off walls of earth dams has been studied. Triaxial compression tests on the specimens in various ages and mix designs under different confining pressures have been done and the stress-strain behavior of such materials and their strength parameter changes have been experimentally investigated. It has been observed that increasing the confining pressures applied on the specimens causes the material behavior to be alike the more ductile materials and the compressive strength increases considerably as well. Moreover, a parametric study has been carried out to investigate the influence of essential parameters on the shear strength parameters of these materials. According to the research, increasing the coarse to fine aggregates ratio leads to the increase of compressive strength of the specimens as well as the increase of the cohesion and internal friction angle of the materials. Furthermore, the bentonite content decrease and the cement factor increase result in an increase of the cohesion parameter of plastic concretes and decrease of the internal friction angle of such materials.

Effect of Natural Wollastonite Microfibers on Early-Age Behavior of UHPC

In this study, the effect of incorporating wollastonite microfibers in ultrahigh performance concrete (UHPC) on its early-age properties was investigated. Wollastonite microfibers were added at 0, 4, 8, and 12% as partial volume replacement for cement. Results show that the early-age properties of UHPC mixtures incorporating wollastonite microfibers are highly affected by the microfiber content and aspect ratio. Increasing the wollastonite microfiber content resulted in a compressive strength comparable to or higher than that of the control mixture without microfibers. Wollastonite microfibers reduced shrinkage strains and increased cracking resistance compared to that of the control mixture. However, no significant improvement in the flexural behavior was achieved with the addition of wollastonite microfibers because of a sudden rupture of microfibers within the matrix. Wollastonite microfibers can act as an internal restraint for shrinkage, reinforcing the microstructure at the microcrack level, and leading to an enhancement of the early-age engineering properties of UHPC matrix. Partially replacing cement with natural wollastonite microfibers leads to a reduction in the cement factor, which represents economic and environmental benefits.

One-dimensional consolidation behavior of cement-treated organic soil

This paper addresses the effects of cement treatment on the one-dimensional (1D) consolidation behavior of a highly organic soil (LOI ∼ 40%–60%, where LOI is the loss on ignition), based on 1D constant rate of strain and incremental loading tests. The effects of Portland cement addition are evaluated for dosages ranging from 8% to 100% by dry mass of soil, corresponding to values of the cement factor of 24 and 296 kg of cement per cubic metre of untreated soil, within the range used in deep mixing practice. Additional parameters investigated are the impact of curing surcharge and duration. The most evident effect of the treatment is the development of a cementation-induced preconsolidation stress: the greater the cement dosage, the greater the preconsolidation stress and the greater the vertical effective stress that can be sustained at any void ratio. The results also provide a consistent picture of the effects of cement treatment on stiffness, hydraulic conductivity, coefficient of consolidation, and creep. Comparison to data obtained for the untreated soil demonstrates the “stable” nature of the structure generated as a result of treatment. The consolidation results are complemented by pH measurements, extraction tests, elemental analyses, and Fourier transform infra-red (FTIR) spectroscopy analyses, which provide insight into the interaction between soil organic matter and cement.

A cementation method of loose particles based on microbe-based cement

Microbe-based cement has been widely reported in recent literatures. It is a new method of consolidating loose fine particles, which relies on the bacterially induced formation of a compatible carbonate precipitation around individual particles and at particle-particle contacts. Materials and cementation procedure are two major factors that influence the cementation performance of microbe-based cement. Besides, there are some other factors related to the performance, such as pH, temperature, metabolism activity, the flushed times of bacterial solution, concentration of substrate and calcium ion, etc., which affect consolidation function. The assessment methods for cementation process are carried out by various techniques. The performance of consolidation loose grains based on microbe-based cement is tested with the help of experiment. In this paper a review is presented on the cementation mechanism of microbe-based cement, techniques utilized to monitor cementation process, the consolidated performance by microbe-based cement and bond factors.

Influence of post pattern and resin cement curing mode on the retention of glass fibre posts

To evaluate the influence of post design and roughness and cement system (dual- or self-cured) on the retention of glass fibre posts. Two tapered and smooth posts (Exacto Cônico No. 2 and White Post No. 1) and two parallel-sided and serrated posts (Fibrekor 1.25 mm and Reforpost No. 2) were adhesively luted with two different resin cements--a dual-cured (Rely-X ARC) and a self-cured (Cement Post)--in 40 single-rooted teeth. The teeth were divided into eight experimental groups (n = 5): PFD--Parallel-serrated-Fibrekor/dual-cured; PRD--Parallel-serrated-Reforpost/dual-cured; TED--Tapered-smooth-Exacto Cônico/dual-cured; TWD--Tapered-smooth-White Post/dual-cured; PFS--Parallel-serrated-Fibrekor/self-cured; PRS--Parallel-serrated-Reforpost/self-cured; TES--Tapered-smooth-Exacto Cônico/self-cured; TWS--Tapered-smooth-White Post/self-cured. The specimens were submitted to a pull-out test at a crosshead speed of 0.5 mm min(-1). Data were analysed using analysis of variance and Bonferroni's multiple comparison test (alpha = 0.05). Pull-out results (MPa) were: PFD = 8.13 (+/-1.71); PRD = 8.30 (+/-0.46); TED = 8.68 (+/-1.71); TWD = 9.35 (+/-1.99); PFS = 8.54 (+/-2.23); PRS = 7.09 (+/-1.96); TES = 8.27 (+/-3.92); TWS = 7.57 (+/-2.35). No statistical significant difference was detected for posts and cement factors and their interaction. The retention of glass fibre posts was not affected by post design or surface roughness nor by resin cement-curing mode. These results imply that the choice for serrated posts and self-cured cements is not related to an improvement in retention.

Concrete aggregate and cement mass content effects on compressive strength

The mass content of aggregate (ma) and of cement (mc) of concrete comprise coefficient calculated as ma/mc. Some methods used for designing of concrete mixtures take into consideration this coefficient. In this paper, concrete mixtures were prepared so that mass of cement, water cement factor and granulometric composition have been varied. Values of the coefficient ma/mc in experimental research ranged between 7,20 in concrete mixtures mixed with 250 kg of cement to 3,60 in concrete mixtures mixed with 500 kg per 1m3. From the aspect of compressive strength of concrete, it has been established that optimum values of the coefficient ma/mc depend on the granulometric composition and water cement factor. At higher water cement factors, larger values of ma/mc coefficient are required to achieve the maximum strength under the given conditions.

Abrasion Resistance of Early-Opening-to-Traffic Portland Cement Concrete Pavements

The research investigation presented herein is intended to study the abrasion resistance early-opening-to-traffic portland cement concrete pavements also known as fast-track concrete. The selected matrices are examined using two categories of opening-to-traffic times (6 and 8 h). Type III portland cement and three different cement factors with and without an accelerating admixture were used. The trial mixtures are examined for plastic properties (slump, air content, bleeding, setting times, and adiabatic temperature), bulk characteristics (demolded unit weight and compressive strength), and resistance to abrasion. Depth of wear and rate of deterioration as functions of matrix proportions, opening-time categories, and testing age (up to 20 min or 0.12 in., whichever is reached first) are determined. The influence of other parameters such as cement factor, curing age, and accelerating admixture on resistance to wear of the selected matrices are discussed. Other properties, namely rate of abrasion, relative gain of abrasion, coefficient of variation, and abrasion index, are examined. Finally, the relationship between the abrasion resistance (depth of wear) and bulk characteristic (compressive strength) at both opening and maturity ages are investigated. The findings of this investigation shall benefit highway agencies and municipalities by providing abrasion resistance data on a wide range of matrix constituents and proportions that may be used for fast-track concrete construction.

Resistance to external sodium sulfate attack for early-opening-to-traffic Portland cement concrete

Abstract The results of a study on sulfate resistance of early opening-to-traffic concretes with accelerating admixture, also known as fast-track concretes (FTC), are presented. A total of 11 concretes made with four different cement factors and three different cement types were investigated at both opening and maturity (28 days) ages. Upon curing, the test samples were immersed in a 5% sodium sulfate solution. Length change, mass loss, and compressive strength were monitored for a period of 270 days to evaluate the performance of the test specimens exposed to severe sulfate attack. The influence of immersion period, curing age and cement type and factor on bulk characteristics and sulfate resistance were evaluated. The study produced FTC with excellent sulfate resistance. Length change of FTC incorporating accelerating admixture increased with increasing immersion age and stabilized within 3 months from initial contact. No mass of concrete residues nor notable strength loss were found in any opening time fast track concretes used in the investigation.

In vivo failure analysis of intramedullary cement restrictors in 100 hip arthroplasties

Background We occasionally noticed excessive distal plug position in our clinical routine of cemented hip arthroplasties. We therefore performed an analysis of risk factors for migration of a biodegradable intramedullary gelatine plug.Patients and methods The performance of a cement restrictor was studied in 100 consecutive cemented total hip arthroplasties implanted with third-generation cementing techniques. In a radiographic analysis anatomical parameters, cement mantle quality, and mechanisms and factors for restrictor failure were evaluated.Results 40 restrictors showed inadequate performance: 5 cases of tilting, 22 cement leakages, 16 excessive migrations, 2 excessive migrations plus leakages, and 1 case of leakage plus tilting. excessive migration (< 5 cm) was more common in large intramedullary canals (p = 0.04) and cement leakage was more common in patients with a proximally located isthmus (p = 0.04). Half of the hips showed a complete or almost complete filling of the intramedullary cavity, which was more often found in operations carried out by experienced surgeons.Interpretation A more reliable plug design should be considered for patients with wide intramedullary canals and a high isthmus, to minimize the risk of plug migration and poor cement mantle quality.

Strength and Wear Resistance of Sand-Replaced Silica Fume Concrete

This investigation evaluates: 1) the influence of silica fume content on the strength and resistance to wear of 3-, 7-, 28-, and 91-day moist-cured concretes made with 0, 5, 10, 15, and 20% silica fume replacing a portion of the fine-aggregate; and 2) the influence of various combinations of curing schemes on the strength and resistance to abrasion of the selected fine aggregate-replaced silica fume concretes. A uniform cement factor of 385 kg/m 3 (650 ld/yd 3 ) and a constant water-cementitious material ratio (w/cm) of 0.325 are used in all trial mixtures. The fresh and bulk characteristics, such as slump, air content, time of setting, bleeding, unit weight, and compressive strength are obtained to characterize the selected matrixes. ASTM C 779, Procedure C, Ball Bearings, is used to evaluate the resistance to wear. The compressive strength and abrasion resistance of the fine aggregate-replaced silica fume concretes cured under a continuous moist-curing condition and various combinations of wet-dry curing cycles are compared. The relationships among depth of wear, compressive strength, percentage of silica fume content, and curing age are also studied. Laboratory test results conclude that both the compressive strength and resistance to wear peaked at 10% silica fume content. Silica fume incorporation in concrete by way of fine aggregate replacement did not alter the samples' compressive strength when subjected to the various combinations of wet-dry curing cycles. When compared with continuous moist curing, the selected cycled wet-dry curing conditions caused a modest reduction in resistance to abrasion that varied with silica fume contents, curing cycles, and curing schedules. There was statistically a significant correlation between the dependent variable (depth of wear) and the independent variables (compressive strength, percentage of silica fume content, and curing age) for the samples aged under continuous moist-curing conditions.

Investigation of amplification characteristics of SRS in acetone enhanced by DCM dye fluorescence

The efficient amplification of stimulated Raman scattering in Acetone enhanced by dicyanomethylene(DCM) dye fluorescence and the amplification characteristics are reported in this paper. Under the various concentrations of DCM, various inte nsities of input Stokes signal and various pump laser intensities, the input and output Stokes wave intensities are measured in the experiment. At the concentration of 2×10-4 mol/L for DCM solution in ethanol, the bigg est enhan cement factor of Stokes wave reaches 57 The higher the intensity of pump l aser or input Stokes signal, the higher the intensity of output Stokes wave, an d if the input Stokes is too high, the enhancement coefficient may decrease, the so-called enhancement saturation.

Experimental study of the mechanical behavior of plastic concrete in triaxial compression

This paper is going to present the results of an extensive experimental parametric study of the mechanical responses of various types of plastic concrete in unconfined and triaxial compression tests. 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. A plastic concrete cut-off wall acts essentially as a barrier to stop or reduce the groundwater flow. In this study the effect of specimen age, cement factor, bentonite content and confining pressure on shear strength and permeability of plastic concrete were investigated. The observed behavior is more and more ductile for increasing confining pressure. It is shown, also, that any increase in confining pressure increases the compressive strength as well as the elastic modulus and the deformability of the specimen. It is shown that an increase in cement factor increases the shear strength as well as the elastic modulus. It is obtained that increase of bentonite content, decreases the compressive strength as well as the elastic modulus. Increasing the age of the specimens causes an increase of the compressive strength as well as the elastic modulus and also the shear strength parameters are affected. Also, it is obtained that increase in confining pressure and cement factor reduces the permeability.

Quantification of the water demand of sand in mortar

The sand type has an important influence on the properties of mortar. By means of an extensive experimental research programme, considering nine different sand types, this influence is characterised and quantified. Two series of mortar tests have been undertaken. A first series with a standard mortar composition, and a second series with a modified composition (by changing the sand cement factor) in order to obtain a certain target value for the workability. The results show a very significant influence of the sand type on the mortar properties, with important consequences regarding mix design. The water demand related with the different sand types is investigated considering some geometric sand properties like fineness modulus, relative specific surface and fictitious weight. However, a better correlation is obtained with the apparent dry density or bulk density of the sand. The apparent dry density proves to be a very important parameter for the estimation of the water demand of the sand as well as for the influence of the sand type on the rheological and strength properties of the mortar.

The effect of basic fibroblast growth factor on bone regeneration when released from a novel in situ setting tricalcium phosphate cement.

The osteostimulative effect of the basic fibroblast growth factor is well known, but it is dose dependent, and release kinetic depends on interactions with the used carrier. The aim of our study was to determine the osteostimulative effect of a composite, consisting of an in situ setting tricalcium phosphate cement and basic fibroblast growth factor. A trepanation defect of 1.5 mm in the femur diaphysis of Sprague-Dawley rats was filled with the in situ setting TCP cement combined with 0, 0.25, 2.5, or 25 microg rh bFGF, an autologous bone graft or left empty. The rats were euthanized after 1 and 3 weeks and examined by radiography, histology, histomorphometry, and bending test. The data were analyzed by the Wilcoxon and Kruskal-Wallis test. All TCP groups with or without bFGF showed a good bony ingrowth with a close bone-cement contact. Osseous ingrowth was not influenced by the addition of the different doses of bFGF as shown by histomorphometry. Also, mechanical strength was not affected. In conclusion, the combination of this in situ setting cement with bFGF is not useful for clinical application. The reason of these negative results remains unclear: the osteostimulative effect of bFGF is well known, and the TCP-cement was used as a carrier for rhBMP-2 successfully. These negative results may be due to a too slow or too fast release of bFGF from the cement.

A rapid cyclic voltammetric method for studying cement factors affecting the corrosion of reinforced concrete

A rapid cyclic voltammetric method for studying the influence of cement factors on the corrosion of embedded iron and steel in hardened cement paste is described. The technique employs a “cement electrode” consisting of an iron or steel wire embedded in a miniature cylinder of hardened cement paste. The rapid cyclic voltammetric method is fast, reproducible, and provides information on the corrosiveness of the pore solution environment surrounding the embedded metal. The usefulness of the method is demonstrated by showing how it can be used to evaluate the threshold chloride content of hardened ordinary portland cement paste at which corrosion begins and by using it to evaluate the relative efficacy of several admixed corrosion inhibitors.