Resistance Of Cement-based Materials Research Articles

Effect of Styrene-Acrylic Emulsion on Crack Resistance of Cement-Based Materials

In this paper, the brittleness coefficient, elastic modulus-to-strength ratio, drying shrinkage and autogenous shrinkage and cracking sensitivity were used to investigate the effect of styrene-acrylic emulsion (SAE) on crack resistance of cement-based materials under ultralow water binder ratio (0.22). Then the pore structures, hydration products and surface morphology were also studied to explore the mechanism of SAE on improving the crack resistance of cement-based materials. Results show that, the addition of SAE significantly reduces the elastic modulus, brittleness coefficient, elastic strength ratio, drying shrinkage and autogenous shrinkage of the specimen. The cracking susceptibility is also decreased by the incorporation of SAE and when the dosage of SAE was 5%, the initial cracking time would be extended by 43 hours. In addition, incorporation of SAE can reduce the amount of pores that have an adverse effect on shrinkage, refine the microstructure and decrease the calcium hydroxide formation and microcracks of cement-based materials. Such results would be expected to provide guidance on enhancing the anti-cracking ability of high-performance cementitious materials by the dosage of SAE under low water-binder ratio in practical engineering.

Using viscosity modifying admixture to reduce diffusion in cement-based materials: Effect of molecular mass

The viscosity modifying admixtures (VMAs) can increase the pore solution viscosity of cement-based materials and thus slow down the diffusion of corrosive chemicals. As a key parameter, the increase of the molecular mass of VMAs can improve the anti-corrosion performance. However, if it becomes too large, the VMAs will significantly increase the bulk viscosity of the solution but do not improve the resistance to corrosive chemicals. Aiming at determining the range of molecular mass in which the resistance of cement-based materials can be optimized, the diffusion behavior of KCl in VMAs solutions with various molecular mass was explored. Then the influence of molecular mass of VMAs on chloride diffusion, mechanical properties, hydration and pore structure development of mortar were systematically investigated. The results indicated that within molecular mass range of 600–1500, VMAs can efficiently reduce the ion diffusion in cement-based materials. After 28 days of exposure, the samples containing 5% of polyethylene glycol (PEG) with the molecular mass of 1000 exhibits the minimum diffusion coefficient, which is 30.00% lower than that of the control group. The steric hindrance, which is mainly dependent on the molecular mass of the organic solute rather than its structure, directly determines the microviscosity of a solution. Although the addition of VMAs unfortunately coarsens the pore structure of mortar, and thus leads to the decrease of mortar strength, this study provides a novel approach to improve the durability of cementitious materials by optimizing the molecular mass of VMAs.

Resistance of cement-based materials against high-velocity small caliber deformable projectile impact

This paper presents an experimental study on the resistance of cement-based materials across a wide range of compositions and material properties, against the impact of 8.0-mm-diameter, 7.8-g-mass, conical-nosed deformable ASSAB XW-42 steel and copper projectiles at velocities of approximately 400 m/s, in terms of the penetration depth. The cement-based materials investigated include cement pastes, mortars, concretes, engineered cementitious composites (ECCs), and ultra-high performance concretes (UHPCs) with compressive strengths from 37.9 to 229.4 MPa and elastic moduli from 18.7 to 108.8 GPa. For the range of relative characteristic properties between projectile and target considered, the relative effective hardness index (REH) is shown to provide a good characterization of the penetration depth as well as the projectile deformation including relative length change, diameter change, and mass loss. For the deformable penetration regime investigated, two sub-regimes are identified corresponding to a decreasing REH, i.e. regime I with projectile penetration mechanism and regime II with projectile deformation mechanism. It is also found that UHPCs exhibit better impact resistance against deformable projectiles than high performance concretes (HPCs) with granite coarse aggregate, whereas a reversed trend is observed when non-deformable projectiles are considered. The experimental results of this study provide insights into the quick estimation of penetration depth and guidance on the selection of protective materials for practical engineering applications.

Leaching Behavior of Hardened Cement Paste with Mineral Admixtures in Deionized Water

Abstract In order to obtain the influence of mineral admixtures such as fly ash and slag on the leaching resistance of cement-based materials in water environments, a conventional leaching experiment on the slice specimens with pure, binary, and ternary cement pastes immersed into deionized water was performed. The dissolved calcium concentration, porosity, microstructure, calcium–silicon ratio (Ca/Si), and phase composition of the specimens were characterized by using ethylene diamine tetraacetic acid titration, saturation-drying weighing, scanning electron microscopy, energy dispersive spectrometry, and X ray diffraction analysis. Results show that more fly ash mixed in the blended cement paste results in lesser dissolved calcium concentration in the solution, slower microstructure deterioration, lower porosity increment, and smaller Ca/Si decrease, while the optimum content of fly ash is 40 %. The partial replacement of fly ash with slag in the binary cement paste can improve its microstructure and slow down its leaching process. The ternary cement paste with 20 % fly ash and 20 % slag has an optimum leaching resistance exposed to deionized water.

Potential accelerated test methods for physical sulfate attack on concrete

There is currently no standard test method to determine the physical salt attack (PSA) resistance of cement-based materials. In this study, several accelerated test methods for PSA were evaluated. This was accomplished by testing concrete mixtures in partial and full immersion in sodium sulfate solutions at different concentrations, temperature, and relative humidity cycling. A total of nine concrete mixtures made from three types of portland cement at three different water-to-cement ratios (w/c) were used in this research to compare each method with materials of different qualities. The results showed that a 5% sodium sulfate solution was too dilute to be used in accelerated PSA testing, whereas increasing the concentration to 10% showed better results. In addition, it was found that damage occurred during low temperatures at high relative humidity compared to high temperatures at low relative humidity. Testing fully immersed specimens in 30% sodium sulfate solution gave the highest mass loss, but the damage was located at the bottom third of the specimens because of a concentration gradient that formed in the solution.

Determining porosity and pore network connectivity of cement-based materials by a modified non-contact electrical resistivity measurement: Experiment and theory

A modified non-contact electrical resistivity measurement is proposed to determine porosity and pore network connectivity of cement-based materials. The porosity of mortar with different water-to-cement ratios was tested by mercury intrusion porosimetry (MIP) and the tortuosity was calculated from pore entrapment volume fraction. The relationship between pore structure and resistivity was studied using the three most commonly used theories. It was observed that the multi-phase phenomenological model can indicate the effect of porosity and pore connectivity on the resistivity of cement-based materials. The parameter m in Archie's Law as an index of pore connectivity can be expressed as a variable that varies with the tortuosity. The parameters in the GEM model are closely related to the nature of the material: the parameter M should be related to the composition of the material and the degree of hydration of the cement, and the parameter t is a variable that varies with the pore connectivity. Based on these theories, equations are derived to correlate the porosity and pore network connectivity to the formation factor of cement based materials. The developed approach thus has a potential to be used as a simple and effective tool for pore structure investigation of cement based materials.

Hardening Performance and Mechanism of Fluosilicate Surface Treatment Agent on Cement-Based Materials

Based on the theory of ecological resources recycling, the effects of matrix quality, surface treatment method, soaking time, age after treatment and fluosilicate cation on hardening cement based materials were investigated by using the byproduct of phosphate fertilizer production namely fluosilicate as the surface treatment agent of cement-based materials and changing different surface treatments. The results showed that the permeation capacity of surface hardener solution , the wear resistance and surface hardness of cement-based materials were significantly improved by the treatments of surface sanding and oven drying. Both surface spraying and submerging methods can promptly increase the hardening effect by more than 20%, manifesting as the rapid improvement of wear resistance in 1 day and the maintenance of that in 7 days. The effective spraying amount and soaking time were 100g/m2-200g/m2 and 6 h, respectively. The fluosilicate surface hardener exhibited better hardening effect than the silicate surface hardener for those matrix materials with different quality, especially for the matrix materials with low compactness. The magnesium fluosilicate displayed the best hardening effect. Besides, the mechanism of fluosilicate and silicate surface hardeners were discussed and compared. The results show that the fluosilicate surface hardener produced crystals and colloids by reacting with cement hydrates to fill the void and improve the compactness, other than the silicate surface hardener which produced calcium silicates by reacting with cement hydrates. As a result, the hardness and wear resistance of cement-based materials are improved, but also the probability of a potential alkali-aggregate reaction is substantially reduced.

Twin-twist effect of fibers on the pullout resistance in cementitious materials

As a part of ongoing research to develop a new type of a twin-twisted steel fiber and characterize its tensile performance in cementitious materials, an initial experimental study was performed to evaluate the pullout behavior of the fiber. Comparative analyses were carried out with straight and hooked-end fibers to examine the twin-twist effect on the pullout resistance of fibers. The maximum and residual pullout capacity, bond strength, and energy absorption capacity were evaluated. The twin-twisted fiber showed higher maximum and residual pullout load compared to the straight and hooked-end fibers. In particular, the new type of the twin-twisted fiber retained the residual pullout resistance until the final failure of the fiber, which could significantly improve the toughness and resistance of cement-based materials.

Advanced External Sulfate Attack Testing and Performance Specifications: Different Sample Geometries Testing

External sulfate attacks induce severe deterioration of concrete because of several phenomena: leaching, precipitation of expansive products, aggregates loss, and cracking. A new methodology has been developed to assess sulfate resistance of cement-based materials. We can actually estimate the nature of leached and precipitated minerals, and the microscopic volume variations due to each of the principal sulfate attack phenomena, from relatively simple monitoring parameters: sample mass, hydrostatic weighing, and the amount of leached hydroxide. Quantitative information is given on the mineralogical volume or mass variations, leading us to a phenomena decoupling and a better understanding of the sulfate attack mechanism. After we established the microscopic volume variation scenario, we defined a new performance criterion, the averaged density, capable to describe the tested sample performance variation according to the sample internal state indications given by this criterion. We applied the developed strategy on three different filled and hollow geometries in order to study the effect of the sample geometry on sulfate attack mechanism. The study shows almost the same degradation mechanism: the same microscopic volume variations entrained by the different sulfate attack phenomena. However the hollow tubes promote different precipitated mineral than the two others geometries, due to the different ionic and pH profiles between filled and hollow samples which affects the nature of formed sulfate minerals.

Use of different barium salts to inhibit the thaumasite form of sulfate attack in cement-based materials

We investigated the effects of different barium compounds on the thaumasite form of sulphate attack (TSA) resistance of cement-based materials when they were used as admixtures in mortars. Moreover, we analyzed the inhibition mechanisms within different types of barium salts, namely BaCO3 and Ba(OH)2, on the thaumasite formation. The control cement mortar and mortars with barium salts to cement and limestone weight ratios of 0.5%, 1.0%, and 1.5% were immersed in 5% (by weight) MgSO4 solution at 5 °C to mimic TSA. Appearance, mass, and compressive strength of the mortar samples were monitored and measured to assess the general degradation extent of these samples. The products of sulphate attack were further analyzed by XRD, FTIR, and SEM, respectively. Experimental results show that different degradation extent is evident in all mortars cured in MgSO4 solution. However, barium salts can greatly inhibit such degradation. Barium in hydroxide form has better effectiveness in protection against TSA than carbonate form, which may be due to their solubility difference in alkaline cement pore solution, and the presence of these barium compounds can reduce the degree of TSA by comparison with the almost completely decomposed control samples.

Tensile Strength versus Toughness of Cement-Based Materials against High-Velocity Projectile Impact

This paper presents a laboratory experimental study on the effect of tensile strength and toughness on the resistance of cement-based materials to high-velocity projectile impact. Three types of cement-based materials with similar compressive strength but different tensile strengths and toughnesses were examined in terms of the penetration depth, crater diameter, and crack propagation in specimens subjected to impact of ogive-nosed projectile with a diameter of 13.35 mm and a mass of 19 grams traveling at velocities of about 650 m/s. The materials evaluated include: (i) a plain high-strength concrete (HSC) with low tensile strength and toughness, (ii) a fiber-reinforced concrete (FRHSC) with high toughness but similar flexural tensile strength as the HSC, and (iii) a polymer cement composite (PCC) with high flexural tensile strength but low toughness. The PCC was developed from a combination of inorganic cements with water-soluble polymers, and it had a 28-day flexural tensile strength of 25 MPa. Results suggest that the toughness was a more important parameter that contributes to the impact resistance of the cement-based materials. Increasing the tensile strength alone, however, did not seem to contribute to the impact resistance of the cement-based materials.

Kombinierte experimentelle und numerische Studie zur schwindinduzierten Rissbildung zementgebundener Werkstoffe / Combined Experimental and Numerical Study to assess Shrinkage Cracking of Cement-Based Materials

Abstract In this contribution, a combined experimental and numerical study to assess the cracking resistance of cement-based materials subjected to desiccation is outlined. Experimentally, the tendency to hygral cracking is determined by means of mortar ring specimens exposed to drying atmosphere. A numerical model based on the nonlinear theory of diffusion and nonlinear fracture mechanics is developed. The relevant hygral and mechanical parameters and laws needed for the model have been determined by means of adequate experiments analyzed by inverse analyses. The hygro-mechanical behaviour of two different types of mortar is studied. Numerical results have been compared to experimental findings. Furthermore, a parametric study has been carried out with the aim to characterize the relevant material parameters influencing shrinkage cracking. It can be concluded that a combination of experimental and numerical methods can play a decisive role in optimizing mortars or concretes with respect to predefined and required material properties. In this way, the durability of concrete structures can be significantly enhanced.