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Concrete is one of the most widely used structural materials next to steel. This justifies a detailed study of the material structure to understand the influence of the production parameters on the properties of the concrete. The pore structure of concretes has a major influence on their practical use, as it impacts their resistance to environmental degradation (e.g., frost resistance). In the present study, I have investigated concrete and cement mortar specimens with different water-cement ratios using micro-CT (or micro X-ray tomography) to determine the pore structure and the pore gap parameters of the specimens. It can be concluded that with an increasing water-cement ratio the overall porosity of the samples and the number of large pores (1 mm3) show a decreasing trend, in contrast, the gap parameter shows an enhancing trend. It can also be concluded that any pore-forming additives cause significant changes in the structure. [ABSTRACT FROM AUTHOR]

Calcium sulfoaluminate (CSA) cements are a promising alternative to Portland clinker, however, a thorough understanding of their properties is needed for their broader use in the industry. One of the topics that requires a good understanding is the effect of the w/c ratio on the properties of CSA cements. To this end, the aim of this paper was to provide research into the effects of a w/c ratio in the range of 0.45–0.6 on the properties of fresh and hardened CSA pastes and mortars. For fresh mortars, consistency and setting time, as well as plastic shrinkage tests, were conducted, and were complemented by hydration heat tests, carried out on pastes. For hardened mortars, tests of compressive and flexural strength and dry shrinkage, as well as SEM photography, were conducted. It was found that, regardless of a higher hydration rate, the increase in w/c ratio decreased flexural and compressive strength, as well as shrinkage, while increasing consistency, setting time, and hydration heat. Also observed was a significant decrease in strength between 3 and 7 days of curing in mortars with a high w/c ratio. It can be concluded that, regardless of the hydration rate, low w/c ratios in CSA mortars provide better properties than high w/c ratios. [ABSTRACT FROM AUTHOR]

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Clinker‐ and resource‐efficient composite cements, with their great variety of concrete technology advantages, suffer most from early compressive strength. The literature postulates that the early cement hydration can be increased by more intensive two‐stage mixing. The extent to which different two‐stage mixing processes can increase the early hydration reactions and thus accelerate the compressive strength development of ternary composite cements containing granulated blast furnace slag and limestone was systematically investigated. In addition, the effects of a reduced w/c ratio were determined. Concrete durability was tested. The results show that reducing the w/c ratio improves the performance of composite cements much more significantly than energy‐intensive and more complex two‐stage mixing processes. [ABSTRACT FROM AUTHOR]

Ultrasonic structural health monitoring of cement paste is of great interest both scientifically and practically, because cement is a complex acoustic medium, whose structure affects the propagation of ultrasound, which offers a great wealth for structural monitoring in a non-viscous fluid. In this paper, the effect of water content on the ultrasonic signal of cement was studied. The immersion transmission technique is used to study the relationship between water content and durability of cement. Therefore, this experimental technique investigates the dispersion curves of cement paste prepared with different percentages of water, based on the ultrasonic signal transmitted through the cement paste recorded at different angular orientations, which allows the durability of the cement paste to be controlled by finding the critical angle in order to calculate the ultrasonic velocity. Overall, the result of this analysis shows that the water content has a significant effect on the ultrasonic velocity and durability of the cement paste. [ABSTRACT FROM AUTHOR]

Modern society requires a large number of metal components manufactured by sand casting, which involves the generation of a waste product known as Used Foundry Sand (UFS), of which approximately 100 Mt are generated on an annual basis. Virtually all UFS is currently landfilled, despite the economic and environmental cost overruns that this entails. Here, the recovery of UFS as fine aggregates for the manufacture of concrete is proposed. Since the presence of UFS will mainly affect the mortar that binds the aggregates in the manufacture of concrete, it was decided to isolate this fraction and study only the effect of UFS in mortars. This study evaluated a total of 32 different mixes combining different W/C ratios varying between 0.5 and 0.7 with 5 replacement ratios of natural sand by UFS: 0, 25, 50, 75 and 100%, respectively. The combined effect was evaluated of the W/C ratio and the replacement ratio on the workability, physical properties, mechanical properties, mechanical durability, and microstructure of the mortars. The incorporation of UFS decreases the workability of the mortars due to the absorption of the residue. For the physical properties of the mortars, density decreased and porosity and absorption increased at all replacement percentages. Flexural and compressive strength decreased when the replacement percentage was higher than 25 wt.%. In terms of mechanical durability, the mortars with UFS showed abrasion marks within the limits of the EN-1338 standard. From the results obtained, it is possible to conclude that the mortars with UFS require a higher amount of water. Therefore, while small replacement levels lead to a slight improvement in the mechanical properties, this trend breaks down for high replacement levels due to the negative effect of the high W/C ratios required. The authors recommend that for replacements higher than 25 wt.% of UFS, the W/C ratio has to be taken into consideration to obtain the same workability as the control mortar, although this decreases the mechanical properties. [ABSTRACT FROM AUTHOR]

The damage rating index (DRI) has proven to be a quite reliable microscopic technique enabling the condition assessment of concrete affected by internal swelling reactions. Yet, very little research has been conducted on the use of the DRI to appraise induced deterioration caused by physical salt attack (PSA) and external sulfate attack (ESA). This study aims to assess the condition of concrete subjected to different salt solutions (i.e. sodium sulfate (Na2SO4), sodium chloride (NaCl), seawater and limewater), and exposure conditions (i.e. partially and fully immersed) through the DRI. Concrete specimens displaying two distinct water/cement ratios (i.e. 0.45 and 0.65) were manufactured and exposed to the above salt solutions for 12 months. Then, the samples were removed from the exposure conditions and prepared for microscopic analysis. The DRI was shown to be an effective technique to assess the condition of PSA- and ESA-affected concrete since different degrees of damage and features were captured for the various exposure conditions studied. [ABSTRACT FROM AUTHOR]

In last decade, the electrical resistivity of fresh concrete has gained significant attention as a performance criterion due to its practical application and the extent of information it potentially provides on fresh properties. This study focused on the effect of variation of water–cement ratio on fresh electrical resistivity of concrete. In addition, influential factors like dosage of several supplementary cementitious materials (SCMs) namely fly ash, slag, silica fume, metakaolin were considered in combination with pumice material. The results showed that at very beginning, the fresh resistivity pattern moves up to the maximum point before dropping down to the minimum point. It was also found that w/c ratio has remarkable impact on any concrete mixture's fresh electrical resistivity and this testing was performed by a bulk resistivity meter using three different w/c ratio of 0.4, 0.44 and 0.5. Statistical analysis showed that pumice, Class F fly ash, slag G120S, silica fume, metakaolin mixtures show considerable increment in fresh electrical resistivity at 0.40 w/c ratio and even at 0.50 w/c ratio compared to 100% ordinary portland cement concrete (OPC). Concrete mixtures with different combinations of SCMs behave differently with various proportions and w/c ratio. Some binary and ternary mixtures show little higher standard deviation (SD) values compared to the OPC mixture at different w/c ratios levels due to wide spread of fresh electrical resistivity data. This outcome proves that the mixtures with higher SD value gained lower resistivity during the initial phase and later attained a higher resistivity value. Additionally, initial, and final setting time of concrete have been computed using fresh electrical resistivity data of all concrete mixtures including the OPC. Results indicated 15% to 25% replacement of pumice in binary and ternary mixtures with other SCMs shows wide variation of setting time. In summary, outcome of this research may help construction engineers in the development of affordable field application testing for wide range of pumice based high-performance concrete mixtures and satisfy the requirement of initial and final setting time of concrete. [ABSTRACT FROM AUTHOR]

Modern society requires a large number of metal components manufactured by sand casting, which involves the generation of a waste product known as Used Foundry Sand (UFS), of which approximately 100 Mt are generated on an annual basis. Virtually all UFS is currently landfilled, despite the economic and environmental cost overruns that this entails. Here, the recovery of UFS as fine aggregates for the manufacture of concrete is proposed. Since the presence of UFS will mainly affect the mortar that binds the aggregates in the manufacture of concrete, it was decided to isolate this fraction and study only the effect of UFS in mortars. This study evaluated a total of 32 different mixes combining different W/C ratios varying between 0.5 and 0.7 with 5 replacement ratios of natural sand by UFS: 0, 25, 50, 75 and 100%, respectively. The combined effect was evaluated of the W/C ratio and the replacement ratio on the workability, physical properties, mechanical properties, mechanical durability, and microstructure of the mortars. The incorporation of UFS decreases the workability of the mortars due to the absorption of the residue. For the physical properties of the mortars, density decreased and porosity and absorption increased at all replacement percentages. Flexural and compressive strength decreased when the replacement percentage was higher than 25 wt.%. In terms of mechanical durability, the mortars with UFS showed abrasion marks within the limits of the EN-1338 standard. From the results obtained, it is possible to conclude that the mortars with UFS require a higher amount of water. Therefore, while small replacement levels lead to a slight improvement in the mechanical properties, this trend breaks down for high replacement levels due to the negative effect of the high W/C ratios required. The authors recommend that for replacements higher than 25 wt.% of UFS, the W/C ratio has to be taken into consideration to obtain the same workability as the control mortar, although this decreases the mechanical properties.

When it is necessary to ensure a function of retaining wall, load-bearing or waterproofing, diaphragm walls are used as the definitive structure to fulfill these requirements. Despite compliance with the normative rules for the preparation of concrete, as the latter are poured over great heights, a migration of water from the concrete takes place that can lead serious concerns about the durability of the diaphragm wall as well as the impairment to the strength and stiffness. The water retention capacity of a foundation concrete is determined from specific tests such as static bleeding testing according to standard ASTM C232 or even according to standard NBN EN 480–4 or also according to the 'Bauer' test of pressure filtration. These tests make it possible to quantify the rate of bleeding but do not provide sufficient understanding of the levels of the physical mechanisms responsible for the migration of water in concrete. For that, an approach is proposed here, resulting from soil mechanics, starting from the theory of one-dimensional primary consolidation of Terzaghi. The investigated concrete was proportioned with different water-cement ratio to promote bleeding. Oedometric tests made it possible to assess the ability of water to move in the concrete (coefficient of permeability) as a function of time for different load cases (self-weight of the concrete at different depths). The results show, whatever the stress applied, a good correlation between the values measured by the pore pressure sensor and the excess pore pressure values determined from the solution of the differential equation for one-dimensional consolidation proposed by Terzaghi. [ABSTRACT FROM AUTHOR]

Cement is widely used in marine concrete, and its resistance to chloride ion corrosion has been widely considered. In this paper, based on a laboratory test, the influence of different hydrostatic pressures, coarse aggregate contents and w/c ratios on the chloride resistance performance is analyzed. Based on COMSOL finite element software, a two-dimensional cementitious materials model is established, and the simulation results are compared with the experimental results. The results show that the penetration depth of chloride ions in cement increases with the increase of the w/c ratio. Under the hydrostatic pressure of 0 MPa, when the w/c ratio is 0.35, the penetration depth of chloride ions is 7.4 mm, and the simulation result is 8.0 mm. When the w/c ratio is 0.45, the penetration depth of chloride ions is 9.3 mm, and the simulation result is 9.9 mm. When the w/c ratio is 0.55, the penetration depth of chloride ions is 12.9 mm, and the simulation result is 12.1 mm. Under different hydrostatic pressures, the penetration depth of chloride ions obviously changes, and with the increase in hydrostatic pressure, the penetration depth of chloride ions deepens. Under the w/c ratio of 0.35, when the hydrostatic pressure is 0.5 MPa, the penetration depth of chloride ions is 11.3 mm, and the simulation result is 12.1 mm. When the hydrostatic pressure is 1.0 MPa, the penetration depth of chloride ions is 16.2 mm, and the simulation result is 17.5 mm. [ABSTRACT FROM AUTHOR]

Changing the water-to-cement ratio is one of the major ways to develop cement slurry with different densities, which in turn will greatly affect the pore structure and mechanical properties of cement slurry. In the current study, the cement hydration model HYMOSTRUC3D was used to investigate the effects of water-to-cement (w/c) ratio (0.40, 0.44, 0.50) on the pore structure evolution and strength development of cement slurry. The microstructure of the cement stone was characterized via scanning electron microscope (SEM) and micro-computed tomography (micro-CT), and the mechanical strength of the cement stone was tested and analyzed via a mechanical tester. The simulated compressive strength and capillary porosity are in good agreement with the measured data, where the relative error between the simulated results and measured results are within 0.6~10.7% and 13.04~25.31%, respectively. The capillary porosity is proved as the main factor affecting the compressive strength of cement stone with different w/c ratios. Herein, the mathematical relationship between the measured capillary porosity and compressive strength could be well fitted via the mathematical prediction models of the Balshin function (R2 = 0.95), Ryshkewitch function (R2 = 0.94), Schiller function (R2 = 0.96), and the linear regression function (R2 = 0.95). Moreover, the linear regression function (y = −2.38x + 82.76) can be used to characterize and predict the quantitative relationship between the compressive strength and capillary porosity of cement stone. The findings in this study will provide a reference value in the fields of oil and gas cementing and building concrete. [ABSTRACT FROM AUTHOR]

The passivation process quality was studied considering polarization periodicity, passivation consolidation parameters, and data processing. Passivation process quality in steel reinforcement affects a structure’s planned future service life. Some research has addressed this phenomenon, but its study is complicated by the limits of analog-era data, dispersion in corrosion rate data, and their interpretation. Two series of small reinforced concrete specimens were built using two water/cement ratios and two curing/storage combinations and exposed to the marine environment. Polarization periodicity did not affect passivation/depassivation during passivation but on the data processing. The curing and storage process influenced the tendency towards depassivation. Post-curing storage type affected the cumulative corrosion rate from 1 to 5 μA*day/cm2; this is equivalent to the margin of uncertainty in interpretation.

• Thestrength of samples carbonation curing for 4h are higher than water curing for 7 d. • The pores larger than 200 nm played a leading role in carbon dioxide diffusion. • The major reactants in the carbonation reaction were C 2 S, C 3 S, and a few (Ca(OH) 2). • The carbonation curing mechanism of hardened cement pastes are discussed. Recently, with the development of accelerating mineral carbonation technology, the preparation of building materials by using carbonation curing cement-based materials has attracted wide attention. The diffusion and transfer mechanism of carbon dioxide in porous cementitious materials was the key point that restricts the improvement of materials carbonation rate. In order to obtain comprehensive information that affects accelerating carbonation rate of porous cement-based materials, this paper talks about the influences of paste porosity controlled by water to cement ratio (w/c) on carbonation and the paste micro-structures evolution. Also, mineral compositions before and after carbonation curing were evaluated. Results show that the carbonation rate, carbonation depth and compressive strength are improved after carbonation, while total porosity of complete carbonation zone decreases with the growth of paste porosity. The pores with diameter larger than 200 nm played a leading role in carbon dioxide diffusion, which were reduced by 84.25% of the total volume after carbonation curing. The carbonization reaction mainly occurred in the first six hours in carbonation curing, while the subsequent carbonation curing were unprofitable to the carbonation effect due to the generation of calcium carbonate prevents the diffusion of CO 2 , making the subsequent carbonation become difficult. XRD results revealed that during carbonation curing the major reactants were C 2 S, C 3 S and some hydration products of Ca(OH) 2 after 1 d hydration. [ABSTRACT FROM AUTHOR]

• PCC cylinders were repeatedly exposed to hydrocarbon fluids and high thermal cycles. • Cylinders experienced saponification and developed scaling on the surface. • The depth of penetration of hydrocarbon fluids into cylinders influenced the depth of scaling. • The w/c ratio of concrete significantly affected saponification process and surface scaling. • Exhaust heat of military aircrafts caused micro to hairline cracks in ordinary concrete. The conventional Portland cement concrete (PCC) aprons that house Air Force and Navy aircrafts are reported to experience significant scaling on the surface, which is a serious concern for the safe operation of military aircrafts. The purpose of this study is to investigate the underlying scientific facts for the scaling of PCC aprons at military airbases. An experimental program was developed to replicate the physical and environmental circumstances that prevail in aprons at military airbases. Standard sized PCC cylinders were repeatedly exposed to aviation oils and high temperature, both simultaneously and separately, until surface scaling became obvious. Chemical analyses were conducted on the aviation oils, scaled concrete as well as on the original PCC; analysis results revealed that aviation oils contain ample hydrocarbon compounds to trigger surface scaling at high temperature. When PCC cylinders were repeatedly exposed to aviation oils and high temperature simultaneously, they underwent a saponification process after a couple of cycles of exposure, and rapidly developed scaling on the surface after subsequent exposures. Saponification increased with the increase in numbers of cyclic exposures and consequently resulted in the development of a significant volume of loose fines on the surface of the PCC cylinders. The repeated saponification and deposition of calcium phosphate (salts) at the top layer caused rapid scaling, by acting together. On the other hand, PCC cylinders that were exposed to aviation oils at ambient temperature neither experienced a saponification process nor developed scaling. The influence of w/c ratio on the saponification, scaling and thermal cracking was examined as a part of the current study. The present study reveals a relationship between the depth of scaling and aviation oils' penetration depth, and the effect of high temperature, microcracks and voids, and their influences on the scaling process of PCC are also reported herein. [ABSTRACT FROM AUTHOR]

Cement is widely used in marine concrete, and its resistance to chloride ion corrosion has been widely considered. In this paper, based on a laboratory test, the influence of different hydrostatic pressures, coarse aggregate contents and w/c ratios on the chloride resistance performance is analyzed. Based on COMSOL finite element software, a two-dimensional cementitious materials model is established, and the simulation results are compared with the experimental results. The results show that the penetration depth of chloride ions in cement increases with the increase of the w/c ratio. Under the hydrostatic pressure of 0 MPa, when the w/c ratio is 0.35, the penetration depth of chloride ions is 7.4 mm, and the simulation result is 8.0 mm. When the w/c ratio is 0.45, the penetration depth of chloride ions is 9.3 mm, and the simulation result is 9.9 mm. When the w/c ratio is 0.55, the penetration depth of chloride ions is 12.9 mm, and the simulation result is 12.1 mm. Under different hydrostatic pressures, the penetration depth of chloride ions obviously changes, and with the increase in hydrostatic pressure, the penetration depth of chloride ions deepens. Under the w/c ratio of 0.35, when the hydrostatic pressure is 0.5 MPa, the penetration depth of chloride ions is 11.3 mm, and the simulation result is 12.1 mm. When the hydrostatic pressure is 1.0 MPa, the penetration depth of chloride ions is 16.2 mm, and the simulation result is 17.5 mm.

Changing the water-to-cement ratio is one of the major ways to develop cement slurry with different densities, which in turn will greatly affect the pore structure and mechanical properties of cement slurry. In the current study, the cement hydration model HYMOSTRUC3D was used to investigate the effects of water-to-cement (w/c) ratio (0.40, 0.44, 0.50) on the pore structure evolution and strength development of cement slurry. The microstructure of the cement stone was characterized via scanning electron microscope (SEM) and micro-computed tomography (micro-CT), and the mechanical strength of the cement stone was tested and analyzed via a mechanical tester. The simulated compressive strength and capillary porosity are in good agreement with the measured data, where the relative error between the simulated results and measured results are within 0.6~10.7% and 13.04~25.31%, respectively. The capillary porosity is proved as the main factor affecting the compressive strength of cement stone with different w/c ratios. Herein, the mathematical relationship between the measured capillary porosity and compressive strength could be well fitted via the mathematical prediction models of the Balshin function (R2 = 0.95), Ryshkewitch function (R2 = 0.94), Schiller function (R2 = 0.96), and the linear regression function (R2 = 0.95). Moreover, the linear regression function (y = −2.38x + 82.76) can be used to characterize and predict the quantitative relationship between the compressive strength and capillary porosity of cement stone. The findings in this study will provide a reference value in the fields of oil and gas cementing and building concrete.

Highlights • DIP was applied to analysis the microstructure. • The relationship between pore size and pore shape was established. • The forming mechanisms of capillary pores was studied. Abstract Pore structure is a significant microstructural characteristic in cement-based materials and dominates the mechanical and transport properties of the materials. In this study, sectional plane analysis based on backscattered electron scanning electron microscope (SEM-BSE) images was used to provide insights into the nature of the pore structure. The effects of the w/c ratio on the total porosity and heterogeneity of the local porosity were analyzed. By coupling using Digital Image Processing (DIP) method, each single pore displayed on SEM-BSE images was captured, and the equivalent circular diameter, hydraulic radius, and roundness of each single pore were calculated to describe its size and shape characteristics. The relationship between the pore size and pore shape was also established by comparing the pore size distribution and the shape parameter distributions. Results indicates that pores become less spherical with increasing pore sizes. Status oriented model was further introduced to simulate the hydration process and investigate the forming mechanisms of capillary pores. [ABSTRACT FROM AUTHOR]

The grey correlation between the factors such as C/S ratio-W/C ratio et al and the performance of cementitious grout such as compressive strength-fluidity et al were studied through grey correlation analysis. The data were processed using initialization and average-respectively. The results show that the correlation between W/C ratio and the 1 d-3 d and 28 d compressive strength of cementitious grout is the highest-followed by the ratio of mortar and the amount of water reducing agent. The influence of C/S ratio and W/C ratio on the fluidity of grouting material is basically the same-and higher than other factors. The effect of C/S ratio on the tensile bond strength of grouting material is the highest. The effect of W/C ratio and water reducing agent on the tensile bond strength of grouting material is basically the same. [ABSTRACT FROM AUTHOR]

In present paper, concrete compressive strength is evaluated using back propagation feed-forward artificial neural network. Training of neural network is performed using Levenberg-Marquardt learning algorithm for four architectures of artificial neural networks, one, three, eight and twelve nodes in a hidden layer in order to avoid the occurrence of overfitting. Training, validation and testing of neural network is conducted for 75 concrete samples with distinct w/c ratio and amount of superplasticizer of melamine type. These specimens were exposed to different number of freeze/thaw cycles and their compressive strength was determined after 7, 20 and 32 days. The obtained results indicate that neural network with one hidden layer and twelve hidden nodes gives reasonable prediction accuracy in comparison to experimental results (R=0.965, MSE=0.005). These results of the performed analysis are further confirmed by calculating the standard statistical errors: the chosen architecture of neural network shows the smallest value of mean absolute percentage error (MAPE=, variance absolute relative error (VARE) and median absolute error (MEDAE), and the highest value of variance accounted for (VAF).

Article presents the results of the effect of humidity on early shrinkage of normal concrete with variable W/C ratio. As known for a long time, shrinkage is dependent of many factors. One of them is the W/C ratio and the quantity of water which is located in the concrete mix. In article there were discussed changes taking place in the concrete mix, the methods of research and the partial results obtained by the authors of the paper. Shrinkage is a phenomenon well known and studied by various research centers. The total amount of shrinkage may depend on various factors such as humidity, temperature, composition of the concrete mix, the W/C ratio, the size of the item. The study was conducted to determine the amount of shrinkage in its early stages. It is very important for concrete floors contractors, precast manufacturers to start at the right time finishing work and prevent the formation of shrinkage cracks.

In this study; the engineering properties of volcanic rocks obtained from four different quarries in the province of Erzincan region in the Upper Euphrates Part in the Eastern Anatolia Region were investigated. In laboratory studies, the experiments including bulk and aggregate tests (bulk and dense unit weight, specific mass, water absorption, Los Angeles test for resistance to wear, freezing resistance and uniaxial compressive strength) were conducted on 5 volcanic samples according to the standards (Turkish Standard, British Standard and ASTM) and in the second stage, grading of concrete tests (grading of the concrete aggregates, concrete preparation, slump test, specific density of concrete, uniaxial compressive strength, modulus of elasticity, splitting tensile strength, abrasion resistance and capillarity) were performed on the concrete samples with volcanic aggregates. For fresh concrete composition, water/cement ratio was selected as the main variable providing homogeneous mixing and the highest strength to the concrete samples with a specific granulometry. Cylindrical concrete samples were produced with a variety of water/cement ratios cured for 7 and 28 days in water and their compressive strengths were assessed in the light of their physical and mechanical properties. The results obtained from aggregates and concrete tests, which were performed in line with the standards showed that especially Yassıtepe-Doğu (YTD) sample, one of the volcanic rocks from Erzincan region can be used as concrete aggregate. It was observed that compressive strength of the concrete samples could satisfy C25/30 strength class and upper classes. In addition, it was understood that they can be used in highways, bridges, dams, buildings etc., especially as structural concrete. [ABSTRACT FROM AUTHOR]

Shrinkage strain, compressive strength and water absorption of high performance concrete (HPC) are estimated to high accuracy with linear equations using the w/c ratio and paste volume as variables. A paste volume reduction, thus an increase in coarse aggregate fraction, improves the HPC properties. These changes most likely result from: 1) adsorption of water on a greater surface of aggregate, leading to bulk paste desiccation and densifying and reduction in actual w/c ratio and width of aggregate-cement paste interfacial transition zone; 2) beneficial influence of larger volume of coarse aggregates produced from rocks of high strength and low water absorption. [ABSTRACT FROM AUTHOR]

In this paper, the relationship between compressive strength and w/c ratio of cement based materials is revisited through the pore features such as mean distribution radius (r 0 . 5 ) and permeable porosity (P). At first, the pore features for different cement based components namely OPC paste, OPC sand mortar, cement-fly ash paste and mortar are estimated as a function of mix factors (i.e. w/c ratio and curing ages) by using the readily available relationships. The relationships between compressive strength and pore features for the above mentioned cement based components are also established. Finally the estimated compressive strength through the pore features versus w/c ratio curves are plotted which resembles the nature of Abrams established relationship between strength and water cement ratio. [ABSTRACT FROM AUTHOR]

Grouting the fractures encountered when constructing underground facilities is of primary importance for environmental, safety and economic reasons. The success of grouting operation, however, depends upon several parameters governing the grout propagation. Experimental benches replicating fractures have therefore been designed to study processes related to grout propagation. In this paper, we investigate the ultrasonic transport properties of such an idealized fracture whose 100 µm aperture is about 0.02 the wavelength, and filled with various fluids flowing under external forcing. As the artificial fracture is made of two solid and parallel walls separated by a thin fluid layer, we use the thin fluid layer concept to study the compressional (P-) wavefield transmitted across and reflected off the fracture, with no mode-conversion considered. We demonstrate that air and various fluids (water, grouts of varied w/c – water to cement ratio) can be distinguished when injected into the fracture, both at atmospheric pressure or under over-pressure as done in real grouting cases in the field. Then, using an analytical solution, we verify our experimental data and predict the results that can be obtained with a different fracture aperture. Our results illustrate that replicating such ultrasonic measurements both in space and time would allow to monitor successfully the grout propagation within an artificial fracture. The detection of the filtration of the suspended cement-particles of the grout, the formation and erosion of filter-cakes, are also in the scope of the method. [ABSTRACT FROM AUTHOR]

Freeze-thaw damage is one of the main deleterious processes of concrete in cold climates. This study intends to detect the ongoing freeze-thaw (FT) deterioration in concrete specimens through the use of the global assessment combining the results of the mechanical and microscopic evaluation, pressure tension (PT) and compressive strength test as well as the Damage Rating Index (DRI), respectively. Concrete specimens displaying two w/c ratios (i.e., 0.65 and 0.45) were cast and subjected to FT cycles (i.e., 1, 5, 10, 20 and 30) and later the mechanical and microscopic assessments were conducted. Results show that PT and DRI are effective and reliable techniques to evaluate the condition of FT-affected concrete displaying various microstructures, since the PT test captures the damage at a very early stage of FT deterioration and DRI could identify important distress features at various stages of FT-affected concrete. Ultimately, the diagnostic nature of the PT test has been validated through the use of DRI. [ABSTRACT FROM AUTHOR]

The hydration kinetics of Class H oil well cement with and without chloride accelerators were evaluated via isothermal calorimetry. A series of tests were conducted with two different water-to-cement (w/c) ratios (0.38 and 0.91) at two different temperatures (15 °C and 25 °C). The test results indicate that the effect of different chlorides on the overall cement hydration rate is primarily determined by the molar concentration of the chloride in water and can be simulated by a generalized scale factor model. At concentrations up to 0.9 M Cl − , the overall hydration rate increases approximately linearly with the CaCl 2 concentration and shows virtually no dependence on temperature and w/c ratio. In contrast, when NaCl or KCl is used at similar concentrations (up to 0.9 M Cl − ), the hydration rate increases linearly with the logarithm of the chloride concentration and the correlation varies slightly with temperature and w/c ratio. [ABSTRACT FROM AUTHOR]

The questions of the extruded concrete composition and the possibilities of modifying it are very important for the technology for the extruded concrete. The gained experience of working with the extruders of hollow core slabs shows that the operators of such equipment frequently choose an improper strategy for the production process. The main drawbacks are as follows: a) the use of fairly stiff mixture that is far above the necessary Vebe consistency class V2 for this technology; b) the over saturation of the mixture with coarse aggregates which determines a low compaction factor of the mixture; c) the rejection of using concrete admixtures which causes equipment overloads or led to its exploitation in the limitary conditions. Besides, the experience of using extruders proves that all parameters predicted by standards and other norms (for example, concrete strength class C40/50 or C50/60 including water cement ratio W/C

• The model can predict well the trend of cracking potential variation in concrete. • Plastic shrinkage cracking in concrete can be decreased by reducing the evaporation-bleeding ratio and accelerating the initial set. • Autogenous shrinkage and restrain degree may affect the model performance. Plastic shrinkage cracking in cementitious materials is caused mainly by rapid and excessive moisture loss during mixture's early ages, before sufficient tensile strength is gained. A novel model has been previously developed by the authors to estimate the severity of plastic shrinkage cracking in concrete. This paper presents findings of a series of full-scale experiments carried out to validate the accuracy of the proposed model. The experiments included investigating the impact of cement type, water-cement ratio (w/c), and admixtures (i.e., accelerator, retarder, and superplasticizer). The tests were performed in three rounds under similar ambient conditions using 3 slabs (3 m × 2 m) and 3 ring test moulds at each round. The results confirm the accuracy of the model in anticipating/comparing the cracking severity of the tested concretes. [ABSTRACT FROM AUTHOR]

This paper gives an introduction to a new form of concrete called foam concrete which is manufactured by mixing a cement paste or slurry with a manufactured foam material. It is a revolutionary new cementing material which is both lightweight and strong. Here the technique of cast in-situ foam concrete preparation, use of fly ash as a filler material in foam concrete and a comparative study of heat insulation capacity of foam concrete to other commonly used construction materials has been presented. The paper discusses the changes in the property of foam concrete because of the use of different graded sands and different water-solid ratios. Its uses and advantages over other construction materials have also been enlisted. [ABSTRACT FROM AUTHOR]

Highlights: [•] Krieger–Dougherty equation could predict the viscosity of blended cement suspensions. [•] The use of mineral additions reduced the effectiveness of cement superplasticizers. [•] Cement with limestone under 30% had little effect on paste rheology. [•] Fly ash lowers the minimum water demand for suitable fluidity. [ABSTRACT FROM AUTHOR]

Abstract: The durability of concrete structures and, consequently, their service life, have improved significantly due to the introduction of pozzolans to the industry; thus, using newly developed pozzolans has become a necessity for the construction of concrete structures, especially in aggressive environments. In the laboratory study presented here, the effects of substituting cement with 10%, 20% and 30% natural zeolite on concrete durability were compared to the effects of substituting 5%, 10% and 15% metakaolin and 5%, 7.5% and 10% silica fume, along with water-to-cement ratios of 0.35, 0.40, 0.45 and 0.50. The comparison is made according to the test results of compressive strength, water absorption, sorptivity, volume of voids, electrical resistance, gas permeability and chloride diffusion, and their inter-relationships also were investigated. Results show that, in general, the zeolite is not as active as silica fume or metakaolin, although it could be used as a substitute for pozzolans because it has better durability characteristics and is economical and environmentally friendly as well. [Copyright &y& Elsevier]

The present study investigated how the aggregate characteristics namely individual size, grade and type affects flowability of mortar mixes. Two types, river sand and crusher dust four single sizes namely 1.18 mm, 0.600 mm, 0.300 mm, 0.150 mm and for single gradation of each fine aggregate were considered in the present research work. In total, 103 mortar batches was made with three different sand to cement ratios [s/c] and two different water to cement ratios [w/c] to find out the flowability of mortar and tested using standard flow table. Out of 103 mortar batches, 52 were with river sand and 51 were with crusher dust. Tests were performed as per ASTM 109 standards. S/c ratio varied from 1 to 3 with an increment of one and w/c ratio was chosen in such a way that all the mixes to give measurable flow. The influence of particle shape and surface texture of aggregate were characterized with an angularity test based on ASTM C1252 in terms of percent of air voids in a loosely compacted fine aggregate. The results indicate that the size of aggregate and uncompacted void content have greater impact flowability of mortar. Mortar made with river sand has got better flowability than that of mortar made with crusher dust due to its higher degree of irregularities. Mortar with higher aggregate content has low percentage of spread compared to mortar with low aggregate content. Similarly, graded aggregate has lesser percentage of spread due to its proper packing compared to single sized aggregates. [ABSTRACT FROM AUTHOR]