Microstructure,physical and mechanical properties of mortar–rubber aggregates mixtures

This work focuses on the feasibility of reusing and valorising rubber aggregates from shredded worn tyres in cement composites. Our purpose is to study the influence of both microstructures of matrix and of interfacial transition zone (ITZ) on mechanical properties of mortar–rubber aggregates mixtures. The same volume of rubber aggregates substituted volume fractions of sand. Volume ratios of rubber aggregates were ranged from 0% to 50%. Micro structural morphology of various samples was observed by means of scanning electron microscopy (SEM). The matrix porosity and the evolution of hydration products (CSH, CaOH₂, CaCO₃) were estimated for specimens that had been curing for 28 days at constant temperature and constant relative humidity. An energy dispersive X-ray analyser and X-ray diffraction were used together with SEM in order to quantify these results.     

Chemical–physical behaviour of matt waste in cement mixtures

The chemical and physical behaviour of matt waste (MW), a by-product which derives from purification processes of cullet from separated glass waste collection, has been studied as new component for cement based materials. Up to now, recycling for MW is not fully exploited. The aim of this research is to investigate the possible benefits of MW addition to cement systems. Investigations on paste samples cured in accelerated conditions were carried out with different analytical techniques (FT-IR, TGA, SEM, MIP) to investigate MW reactivity with portlandite and its effect on pastes microstructure. The results highlight pozzolan behaviour of MW at long curing time and a refinement of porosity leading to a compact microstructure.     

Dependence of ceramics physical–mechanical properties on chemical and mineralogical composition

To determine the dependence of physical–mechanical properties of ceramics on chemical and mineralogical composition, the appropriate raw materials have been tested and five batches of ceramic specimens have been formed. The aforementioned specimens have been made of the following components: fusible clay, quartz sand, chamotte, sawdust and crushed window glass. The specimens differed by the amount of the components (differences in burning regime were insignificant). After having formed and burned the specimens, their X-ray phase analysis has been carried out, elemental chemical composition has been defined and the composition of chemical oxides has been calculated. Moreover, the following physical–mechanical properties have been determined: density, general contraction and compressive strength. The test results showed that the physical–mechanical properties of ceramics mostly depend on the amount carbon, silicon and aluminum. The mineralogical structure of specimens under testing was practically unchanged.     

Effects of urea–formaldehyde resin mole ratio on the properties of particleboard

The use of urea–formaldehyde (UF) resins with lower contents of free formaldehyde in the board industry has led to products with very low emissions of formaldehyde. This study gives a detailed account of the influence on the mechanical and physical properties of the particleboard using UF resins with different mole ratios of formaldehyde:urea within the range 0.97–1.27. The mole ratio influenced not only the thickness swelling (TS) and water absorption (WA) but also the internal bond strength (IB) and the modulus of rupture (MOR) if the manufacturing process was optimized. The investigation revealed clearly that at mole ratios of formaldehyde giving the emission class El the MOR, IB, TS, and WA of particleboard deteriorated. Compensation for the deterioration could be provided through a higher dosage of resin or through the modification of UF resin. However, both alternatives meant that the product would be more expensive.     

Effect of Bermuda grass root on mechanical properties of soil under dry–wet cycles

Bulletin of Engineering Geology and the Environment - It has been proved that Bermuda grass root is an effective material to improve the mechanical properties of soil, but the effect of the...     

Effects of lime treatment on the microstructure and hydraulic conductivity of Héricourt clay

This study aims at evidencing the effects of lime treatment on the microstructure and hydraulic conductivityof a compacted expansive clay, with emphasis put on the effect of lime hydration and modification.For this purpose, evolutions of hydraulic conductivity were investigated for both lime-treatedand untreated soil specimens over 7 d after full saturation of the specimens and their microstructureswere observed at the end. Note that for the treated specimen, dry clay powder was mixed with quicklimeprior to compaction in order to study the effect of lime hydration. It is observed that lime hydration andmodification did not affect the intra-aggregate pores but increased the inter-aggregates pores size. Thisincrease gave rise to an increase of hydraulic conductivity. More precisely, the hydraulic conductivity oflime-treated specimen increased progressively during the first 3 d of modification phase and stabilisedduring the next 4 d which correspond to a short period prior to the stabilisation phase. The microstructureobservation showed that stabilisation reactions took place after 7 d. Under the effect of stabilisation,a decreasing hydraulic conductivity can be expected in longer time due to the formation ofcementitious compounds.
2014 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting byElsevier B.V. All rights reserved.     

Effect of polyurethane on the stability of sand–clay mixtures

Three types of polyurethane were synthesized from mixtures of toluene diisocyanate, polyethylene glycol and polypropylene glycol for use in soil stabilization to improve the erosion resistance. The three polyurethanes were tested at different aqueous concentrations and sand:clay mixtures at weight ratios of 1:1, 1:3 and 1:5. The results of the rainfall simulation, unconfined compression and direct shear tests showed that the polyurethanes improve both strength and erosion resistance significantly. The observed improvement in soil erosion resistance is attributable to the physico-chemical interaction of the long-chain macro-molecules of polyurethane with the clay fraction of the soil.     

Investigation of the effects of wetting–drying and freezing–thawing cycles on some physical and mechanical properties of selected ignimbrites

This study was performed to investigate the changes in the physical and mechanical parameters of ignimbrites of different colors (black, red, yellow, gray) from Central Anatolia under the influence of wetting–drying and freezing–thawing cycles. For this purpose, 96 NX-size core samples were prepared. The unit weight, specific gravity, apparent porosity, water absorption by weight, slake durability index, uniaxial compressive strength, and P-wave velocity of each ignimbrite sample before conversion were determined. All of these parameters were then redetermined every 10 cycles (for a total of 50 cycles) for each sample. The changes in the values of the parameters after these set numbers of cycles were evaluated statistically. The petrographic and chemical compositions of the volcanic rocks influence their physical and mechanical properties, so some changes were also observed in the ignimbrite samples after these physical processes. Freezing and thawing cycles were observed to have an obvious impact on the physical and mechanical properties of the samples. The greatest changes were observed in black ignimbrite (with ferromagnesian minerals).     

Physical and mechanical properties of durable sisal fiber–cement composites

Sisal fiber–cement composites reinforced with long unidirectional aligned fibers were developed and their physical–mechanical behavior was characterized in the present study. Flat and corrugated sheets were cast by a manual lay-out of the fibers in a self-compacted cement matrix and compressed with a pressure of 3 MPa. Direct tensile and bending tests were performed to determine the first crack, post-peak strength and toughness of the composites. Drying shrinkage, capillary water absorption and water tightness tests were performed to characterize the physical properties of the composites. To ensure the composite durability, the ordinary Portland cement matrix was modified by adding metakaolin and calcined waste crushed clay brick to consume the calcium hydroxide generated during Portland cement hydration. The durability of the newly developed composite was determined through accelerated aging conditions using the hot-water immersion test. The developed material presented a multiple cracking behavior under bending, even when subjected to 6 months of hot-water immersion under 60 °C. Scanning Electron Microscopy was used to investigate the micro-structure of the composites before and after aging.     

Generalized stress field in granular soils heap with Rayleigh–Ritz method

The stress field in granular soils heap (including piled coal) will have a non-negligible impact on the settlement of the underlying soils. It is usually obtained by measurements and numerical simulations. Because the former method is not reliable as pressure cells instrumented on the interface between piled coal and the underlying soft soil do not work well, results from numerical methods alone are necessary to be doubly checked with one more method before they are extended to more complex cases. The generalized stress field in granular soils heap is analyzed with Rayleigh–Ritz method. The problem is divided into two cases: case A without horizontal constraint on the base and case B with horizontal constraint on the base. In both cases, the displacement functions u(x, y) and v(x, y) are assumed to be cubic polynomials with 12 undetermined parameters, which will satisfy the Cauchy's partial differential equations, generalized Hooke's law and boundary equations. A function is built with the Rayleigh–Ritz method according to the principle of minimum potential energy, and the problem is converted into solving two undetermined parameters through the variation of the function, while the other parameters are expressed in terms of these two parameters. By comparison of results from the Rayleigh–Ritz method and numerical simulations, it is demonstrated that the Rayleigh–Ritz method is feasible to study the generalized stress field in granular soils heap. Solutions from numerical methods are verified before being extended to more complicated cases.     

Seismic evaluation of soil–foundation–superstructure system considering geometry and material nonlinearities of both soils and structures

In this paper, in order to increase the accuracy of numerical simulations using finite element methods related to soil–structure interaction problems, the influence of the geometric and material nonlinearities of structures was carefully investigated. By introducing proper models dealing with the geometric and material nonlinearities of structures, the authors have proposed a numerical method for the modeling of the nonlinearity of soils that have been carefully investigated in past research, and also for the modeling of structures based on finite deformation schemes. The accuracy of the numerical analysis related to the structures was firstly verified with an Abaqus (2008) calculation. The calculation was conducted with a program named DBLEAVES (Ye, 2007, Ye, 2011). Furthermore, 2D soil–water coupled dynamic analyses, in the finite deformation schemes of both soils and structures, were conducted on a soil-group pile foundation–superstructure system to investigate the seismic behavior of an elevated bridge during a major earthquake, in which strong nonlinear behavior of geometry and material are expected for both the soils and the structures. The applicability of the proposed numerical method to soil–structure interaction problems encountered in many fields of geotechnical and structural engineering was carefully checked. The main purpose of the research is to propose a numerical method by which it is possible to describe the soil–structure interaction problems with a level of accuracy that can satisfy the needs of both the geotechnical and structural engineering fields.     

Effect of freeze–thaw and thermal shock weathering on the physical and mechanical properties of an andesite stone

Natural stones are exposed to physical weathering due to freeze–thaw (F–T) and thermal shock (TS) when they are used as pavement, cladding and masonry material. In this study, the deterioration of andesite was investigated by determining the physical and mechanical properties of andesite samples after each 10 cycles of F–T and TS up to 50 cycles. It was found that the P-wave velocity, Schmidt hardness and compressive strength decrease to different extents with F–T and TS while porosity and water absorption increase with F–T cycles but decrease with TS cycles. The results showed that F–T has a more destructive effect on the studied material than TS, although abrasion loss measurements suggest that the effect on the surface of the material is greater with TS. An exponential model is proposed to predict the variation of material properties with F–T and TS cycles.     

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.     

Experimental investigation on surface radiation properties’ degradation of solar collector receiver tube material

In this study, we have investigated the degradation characteristics of surface radiation heat transfer properties of stainless steel 304. The emissivity (ε) and absorptivity (α) of stainless steel has been measured for a surface unexposed to sunlight and that exposed to sunlight for various time intervals (240, 480, 720, and 960?h). The temperature dependence of these properties is also measured for the temperature range of 30–300°C at 10 equal intervals. It is observed that the emissivity of the material increased when it is exposed to sunlight and the temperature dependence is very strong beyond 180°C. The absorptivity of the material increases first and then starts to decrease with exposure time. The combined effect of decrease in absorptivity and increase in emissivity leads to reduction in aS/E ratio, which results in a higher rate of radiation loss for exposed surfaces when compared to that for the unexposed surfaces.     

Improving hydraulic properties of lime–rice husk ash (RHA) binders with metakaolin (MK)

To improve long-term hydraulic properties of binders from RHA and lime, 25–75% MK was added to RHA. Binders were formulated and properties were compared to that containing RHA or MK as only pozzolans. The lime–pozzolan ratio was 1:3. The properties tested after 7, 28 and 56 days were: absolute density and fineness of the binders, initial setting time, chemical and mineralogical composition of hydrated binders, flexural and compressive strengths and water absorption of mortars. The micrographs of the hardened binder pastes at 56 days permitted to evaluate the densification of different matrixes and the development of pores. From the results obtained, it was concluded that, MK increased the density of mixtures and decreased their grindability. The presence of MK decreased the SiO₂ content of binders and increases their Al₂O₃ and Fe₂O₃ contents. Calcium-silicate hydrates (CSH) gel and gehlenite (C₂ASH₈) were the main phases formed during the pozzolanic reaction in the presence of MK. No reduction in flexural and compressive strengths was observed after 28 days for binders containing MK. The mixture of 25% MK and 75% RHA which is recommended gave flexural and compressive strengths higher than binder with RHA or MK as the only pozzolan. Water absorption of mortars was less than 20%.     

Electromagnetic properties of the ground: Part II – The properties of two selected fine-grained soils

In Part I of this paper it was established that electromagnetic signal velocities, for instance as used in ground penetrating radar use, are related to the geotechnical properties of Liquid Limit, dry density and percentage linear shrinkage. It was thus established that such geophysical techniques potentially provide an insight into the geotechnical properties of fine-grained soils, as well as illustrating the equal potential of informing radar survey planning and data interpretation through prediction of soil geophysical properties from geotechnical data. In order to extend that research, the work described herein aimed to consider how signal velocities relate to the wide variations in water contents that may occur for a soil in the field, from oven dry to more than 90% by volume. Through the use of time-domain and frequency-domain measurement techniques, data were obtained that allow consideration of soil effects on commercial water content measurement systems and radar equipment. Potentially the most important outcome is that the data indicate that the three geotechnical states (friable, plastic and liquid) give rise to three different signal velocity/water content relationships. In the friable state, the relationship shows large increases in apparent permittivity (as a proxy for signal velocity) with water content, together with increasing electromagnetic dispersion (i.e. variations in velocity with frequency). In the more common plastic state, often not fully considered in the literature, apparent permittivity is shown to increase almost linearly with water content at high frequencies, but in fact can decrease at lower frequencies. This anomaly is explained by the reduction in electromagnetic dispersion caused by reducing dry density. For the liquid state, the relationships are shown to be similar to the plastic state, but with a step increase in apparent permittivity potentially related to soil pore sizes exceeding a critical limit. It is also shown that the plastic and liquid state linear relationships are related to similar trends in the apparent permittivity of the water phase. It is concluded that, when considered over very wide water content and signal frequency ranges, the electromagnetic properties of soils are complex but can be related to geotechnical states and properties. It is, therefore, proposed that the research detailed herein provides a useful initial step in the creation of an electromagnetic properties database of relevance to underground space development.     

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.     

Influences of mixture composition on properties and freeze–thaw resistance of RCC

The paper reports a series of lab investigations carried out on roller compacted concrete (RCC) mixtures containing a wide range of cement contents (100 and 450 kg/m³). The key objectives were to appreciate the effects of variations in the cement content and air entrainment on basic physical, mechanical properties and freeze–thaw (F–T) resistances of RCC mixtures. The Vebe consistency, moisture–density relations, water absorption, permeable voids, compressive strength, and F–T resistances of comparable mixes were evaluated. Physical and mechanical properties indicated a significant deviation from the behavior shown by conventional concrete. Air entrainment was found to be affecting the strength and F/T durability of the mixes. Further analysis shows wide range applications of RCC in various pavement applications.     

Utilization of copper tailing for autoclaved sand–lime brick

The influences of the batch ingredients and the autoclaving processes on the properties of autoclaved sand–lime brick from low SiO₂ content copper tailing were studied. The results show that the copper tailing with low content of SiO₂ can be used to produce autoclaved sand–lime bricks meeting GB11945-1999 for Mu 15 sand–lime brick, if only the proportion of the copper tailing in the brick batch does not exceed 50% (% by mass) and appropriate proportions of river sand and sand powder are added to compensate for the low SiO₂ content. XRD and SEM analyses show that the main hydrothermal reaction products in the brick are 0.9 nm, 1.1 nm and 1.4 nm tobermorite phases, and the andradite in the copper tailing nearly does not take part in the autoclaving reaction.