Effects of water–cement ratio and curing time on the critical pore width of hardened cement paste

Mercury intrusion porosimetry (MIP) test is one of the techniques that have been widely used for analyzing the pore size distribution of hardened cement paste (hcp) and also for the determination of the critical pore width. This study presents the test results of the MIP experiments obtained for three different hcp specimens with the water–cement ratios of 0.26, 0.34, and 0.42 which had been cured for 7, 28, and 365 days under water. Thus, the effects of water–cement ratio and curing time on the critical pore width of hcp were investigated. Test results have shown that, within the limits of the work, and in case of complete hydration, the critical pore width of the hcp seems to be independent of water–cement ratio and is of the order of 25 nm. This value can be considered as the critical pore width of the portland cement gel.     

The influence of moisture on the deformability of cement–polymer adhesive mortar

Adhesive mortars are widely used to set porcelain stoneware tiles on buildings because their bond strength and flexibility properties increase the cladding serviceability. However, their long-term performance is not well understood, mainly the degradation of the polymeric matrix.The influence of moisture content on the flexibility of six adhesive mortars is investigated, based on standard EN 12002. Four of them have defined formulations and the other two are commercial and are widely used to set porcelain stoneware tiles on building façades in Brazil.The results show that moisture content above 6% is sufficient to reduce 50% of the mortar deformability, but that the drying process allows it to recover to a value similar to that prior to saturation; a logarithmic function best fits the correlation between moisture content and flexibility; water immersion increases matrix rigidity.It is suggested that standards should consider flexibility tests on both dried and wet samples as a requirement for polymer-modified mortars.     

Effect of styrene–butadiene rubber latex on the chloride permeability and microstructure of Portland cement mortar

We evaluated the chloride permeability and microstructure of Portland cement mortar modified by styrene–butadiene rubber (SBR) latex, using mortar samples with various polymer/cement (P/C) mass ratios. The incorporation of SBR improved the chloride penetration resistance along with the general ionic permeability of the mortar, while increasing its ionic transport resistance and decreasing its electric capacitance. These data suggest that admixing SBR led to denser and more refined microstructure of the cured cement mortar. Field-emission scanning electron microscopy images confirmed such improvements in the pore structure and the formation of an interpenetrating network structure of SBR and cement hydrate phases at relatively higher P/C ratios. Besides slightly reducing Portlandite content and mitigating carbonation with the increasing P/C ratio in mortar, SBR was also found to promote the formation of calcium aluminate trisulfate hydrate phases and facilitated chloride binding.     

Effects of fineness of cement on polynaphthalene sulfonate based superplasticizer–cement interaction

The effects of fineness of portland cement procured from six different Turkish cement plants, on superplasticizer/cement interaction were investigated. CEM I 42.5 type portland cements (PC) were ground into different finenesses ranging from 280 to 550 m²/kg Blaine values. The effects of PC fineness on initial fluidity and fluidity loss of superplasticized cement paste were evaluated. It was found that increasing the Blaine fineness of incompatible cement up to a certain level reduced the viscosity of cement pastes but had no marked effect on the yield stress of the paste mixtures. Nevertheless, flow loss and also saturation point at 60 min increased with increasing the cement fineness. In other words, pastes with lower viscosity can be produced by using finer cement and more superplasticizer.     

Particle shape effects on the cyclic shear behaviour of the soil–geogrid interface

The accurate determination of the interface shear strength is essential in the design of geosynthetic-reinforced soil structures. The particle geometries of three types of soil materials and a spherical granular medium are imaged and quantified using binary image-based methods and described in terms of regularity. Cyclic direct shear tests are conducted to investigate the effects of particle regularity on the interface shear strength, stress–displacement relationship, shear stiffness, and damping ratio. The results reveal that the interface shear strength and deformation strongly depend on particle regularity. The vertical displacement ratio is found to increase with particle regularity under the same cycle number. The interface stiffness is observed to increase with the cycle number for particle regularities of 0.453, 0.565, and 0.672 but decreases with the cycle number for a particle regularity of 0.971. For a given regularity, the trend of damping ratio with the increasing cycle number is contrary to the that of shear stiffness. Finally, it is observed that the cyclic friction angle decreases with increasing particle regularity, the relationship of which is determined using linear regression. Thus, the systematic quantification of particle shape characteristics can lead to a better understanding of soil–geogrid interface behaviour.     

Effect of water–silt composite blasting on the stability of rocks surrounding a tunnel

This paper describes a new method using water–silt composite blasting for tunneling and the field tests conducted in the Tieshanping tunnel, Chongqing City, China. In this method, water–silt composite is substituted for the traditional pure silt stemming of the blast holes. Because of the incompressibility of water, the attenuation of the blasting wave is postponed and the effect of the blast air extended. The water–silt blasting method resulted in a larger crack zone, improved the breakage of rock, reduced the rock heap, lowered the dust and saved explosive. The stability of the surrounding rock was studied using theoretical analysis, in situ measurements and numerical modeling. The measured displacement at the tunnel crown was in good agreement with the theoretical and numerical results.     

Compression–shear strength criterion of coal–rock combination model considering interface effect

Surrounding rocks around coal tunnel in western mining area of China are typical composite structures composed of weakly cemented soft rock and hard coal, and the tunnel stability is closely related to the overall mechanical behavior of the combination body. The equivalent homogeneous model of coal–rock combination body and its stress state expressions were firstly established based on the strain energy equivalency principle. Then, the general compression–shear failure criterion of the equivalent model which takes into account the cohesive strength of the interface between coal and soft rock was derived by assuming that the yielded mediums all met Mohr–Coulomb criterion. Furthermore, accuracy of the proposed analytical model was verified by carrying out laboratory test for coal-mudstone specimen, and it found that the theoretical results were in good agreement with the test values. Strength of the combination body lies between the strong body and weak body. Finally, the effects of interface cohesion strength, rock thickness and stress level on the failure behavior of combination model were analyzed based on the analytical model. Results show that the proposed model not only contains the classical sliding failure theory for two-dimensional weak plane presented by Jaeger, but also reflect strength behavior of a more complex composite model composed of different rock mediums and structural plane. Thus, the analytical model provides theoretical basis for further studying the mechanical behavior of coal–rock combination model.     

Influence of initial dry density and water content on the soil–water characteristic curve and suction stress of a reconstituted loess soil

In the northwest of China, many loess landslides have occurred without clear triggering factors (i.e., rainfall, earthquake, human activities, etc.). To better understand and analyze the hydro-mechanical properties of these slopes and then provide evidence for their stability analysis subjected to matric suction, it is essential to clarify the soil–water characteristic curve (SWCC). In this study, we conducted a set of experimental trials to examine the influences of initial dry density, water content upon the SWCCs of a loess soil taken from a loess landslide area, by using a conventional volumetric pressure plate extractor. Two common SWCC models have been investigated to evaluate which one is better for loess soil. The suction stress characteristic curves (SSCCs) were also estimated and analyzed. We found that behaviors of SWCCs would be different when the matric suction was greater than a certain value. The two SWCC equations have approximately the same performance in describing the SWCC. The rates of desorption decrease and residual water content increases with increasing the initial dry density, while the initial dry density has little, if any, influence on the air-entry value (AEV). The specimen compacted under higher initial water content would exhibit a higher AEV value and residual water content but lower rate of desorption as compared with the lower initial water content. The magnitude of suction stress had an approximately linear relationship with matric suction before the AEV value, the SSCC shapes will be markedly varied with the initial dry density and water content.     

Ponded infiltration and spatial–temporal prediction of the water content of silty mudstone

Bulletin of Engineering Geology and the Environment - Ponded infiltration is very common in silty mudstone and has a great influence on the stability of related slopes, road cuttings, and tunnels....     

Effect of mixed in crystallization inhibitor on resistance of lime–cement mortar against NaCl crystallization

Salt crystallization is a common cause of damage to porous building materials. Recent research has shown that some chemical compounds may inhibit salt crystallization or alter the mode of crystallization, thus limiting salt damage development, provided that the inhibitor was introduced prior to salt crystallization. In this paper, a pilot study is presented in which sodium ferrocyanide, a crystallization inhibitor for sodium chloride, has been mixed in a lime-cement mortar. Salt resistance of the mortar has been tested by means of a crystallization test. The results of the crystallization test show that the addition of the inhibitor significantly improves the salt resistance of the mortar. Scanning electron microscope observations carried out on the surface of the cross section of the specimens demonstrate that the inhibitor modifies the habit of the salt crystals, as well inhibits the development of specific crystal faces.     

Influence of salt on desorption isotherm and hygral state of cement mortar – Modelling using neural networks

The durability of most porous building materials is strongly related with moisture and salt transport mechanisms. The main storage parameter which describes the hygral state of any porous material is the sorption isotherm. The degree of saturation of pores with moisture phase as a function of relative humidity and salt concentration was determined by means of saturated salt solution method for cement mortar. Then, using feed-forward neural network the relation was approximated for the whole range of arguments. Moreover, both partial derivatives were calculated using specialized neural network approach. It turned out, that a surprisingly simple, layered network (2–4–1) fits well the experimental data. The appropriate subroutines were implemented in HMTRA_SALT code. Using it, the examples of drying of the wall with and without salt were calculated and the results were analysed.     

Effect of sepiolite on retention and drainage of suspensions of fiber–reinforced cement

This research is focused on the study of the effect of rheological grade sepiolite on flocculation, retention and drainage of fiber–cement suspensions by using a focused beam reflectance measurement probe and a vacuum drainage tester. Results show that the sepiolite could be used in the manufacture of fiber–cement to increase the retention of solids and the drainage rate especially in mixtures containing poly(vinylalcohol) fibers.     

Effects of various admixtures and shear keys in wood–concrete composite beams

Wood–concrete composite beams are a layered system, which essentially utilize a concrete layer in compression and a wood layer in tension. This layered system offers a way to construct or rehabilitate wood floors in historic timber structures while increasing the floors’ stiffness and load carrying capacity. This research paper investigates past problems with poor consolidation of the concrete, transverse shrinkage cracks in the concrete, swelling of the wood, moisture loss from the concrete, and the resulting reduced composite efficiency. The research presented herein describes how these problems can be mitigated and thereby increase the composite efficiency of the wood–concrete composite system. By painting the specimens with a water proofing paint, the swelling of the wood can be reduced, which helps to maintain a tight interface between the wood and concrete. To improve consolidation, a self-leveling concrete was designed with a 28-day compressive strength of 34.5 MPa and a slump of 279.4 mm. Nylon fibers and Type I steel fibers were used as admixtures to the fresh concrete to determine their effect on the composite efficiency and the reduction of shrinkage cracks. Twelve full size specimens were constructed and tested to failure. It was found that the most common mode of failure was combined bending and tension at mid span in the wood. An average composite efficiency of 83.4% was reached in the full size test specimens when placed in four point bending.     

Experimental investigation on seepage erosion of the soil–rock interface

Bulletin of Engineering Geology and the Environment - Internal erosion under seepage flow affects the hydraulic and mechanical behavior of the soil, which is one of the most important factors of...     

A study on the mechanical behaviour of cement–bitumen treated materials

Full depth reclamation (FDR) of asphalt pavements has gained general appreciation because of its technical, economical and environmental advantages. Along with FDR, the use of cement–bitumen treated materials (CBTM) rapidly increased over the last 10 years even if the lack of well-established technical specifications and reliable in situ control procedures hinder the cost-effective use of this material. Specifications for CBTM are currently based on experience and do not consider all the relevant parameters that affect the mixture behaviour. In this study the influence of curing conditions, temperature and moisture on the mechanical behaviour of CBTM is investigated. The recycled material was sampled during the FDR operations carried out on the Italian A14 motorway. The effect of curing and temperature on stiffness, and resistance to repeated loading were evaluated using cyclic indirect tensile tests. Moisture susceptibility was assessed by means of indirect tensile strength tests. Results showed a temperature-dependent behaviour of CBTM and allowed to define a simple model to predict the stiffness modulus based on curing time and temperature. In addition, the resistance to repeated loading proved to be a significant factor for the mechanical characterization of tested materials. Finally, regardless of curing conditions, the mixtures showed good moisture resistance.     

The effect of the proportion of thin film transistor–liquid crystal display (TFT–LCD) optical waste glass as a partial substitute for cement in cement mortar

In the high-tech industry in Taiwan, the use of LCD glass products have increased significantly in recent years, which produces a large amount of waste LCD glass during the manufacturing process. This study is based on the 0.485 w/b and 10%, 20%, 30%, 40%, and 50% substitution amount to discuss the effect of glass powder proportions on cement in cement mortar. The research found that of cement mortar by the waste liquid crystal glass powder substitution cement, along with the substitution quantity increase, the set time decreases progressively also the compressive strength gradually reduces. A 10% substitution amount is considered the best in durability tests involving sodium hydroxide, sodium sulfate, and concentrated sulfuric acid resistance. According to the microstructure, the internal structure of the mortar body appears rather dense on the 28th day. Thus, this compound can be used as a substitute for cement and achieve goals of resource development and utilization as well as environmental protection.     

Effects of pre-existing cracks and infillings on strength of natural rocks – Cases of sandstone,argillite and basalt

This study aims to examine the influence of pre-existing discontinuities on the strengths of four natural rocks of different origins. A series of unconfined compression tests was performed on specimens of two types of sandstones, argillite and basalt that contain open and filled cracks. It was found that the presence of cracks tends to decrease the overall strength for all studied rocks; however, the magnitude of strength reduction is related to the property of rock. The larger strength decrease was observed for the relatively harder argillite and basalt, compared to the softer sandstone. It was also found that the infill material could increase the strength of rock specimens, while the obtained strength depended on the characteristics of the fill material.     

Numerical modeling of the effects of roughness on flow and eddy formation in fractures

The effect of roughness on flow in fractures was investigated using lattice Boltzmann method (LBM). Simulations were conducted for both statistically generated hypothetical fractures and a natural dolomite fracture. The effect of increasing roughness on effective hydraulic aperture, Izbash and Forchheimer parameters with increasing Reynolds number (Re) ranging from 0.01 to 500 was examined. The growth of complex flow features, such as eddies arising near the fracture surface, was directly associated with changes in surface roughness. Rapid eddy growth above Re values of 1, followed by less rapid growth at higher Re values, suggested a three-zone nonlinear model for flow in rough fractures. This three-zone model, relating effective hydraulic conductivity to Re, was also found to be appropriate for the simulation of water flow in the natural dolomite fracture. Increasing fracture roughness led to greater eddy volumes and lower effective hydraulic conductivities for the same Re values.