Search

The effect of partial replacement of sand by fine crumb rubber on the impact load performance of concrete was investigated experimentally and numerically. Specimens were prepared for 5, 10 and 20 % replacements by volume of sand. For each case, three beams of size 400 × 100 × 50 mm were loaded to failure in a drop-weight impact machine by subjecting it to 20 N weight from 300 mm height, and similar beams were tested under static load. In both cases, the load-displacement and fracture energy were studied. The dynamic beam behavior was also analyzed numerically using the finite-element method based LUSAS V.14 software. It was found that, the impact tup, and inertial and bending loads increased with increase of sand replacement by fine crumb rubber, while the static peak bending load always decreased. The rubberize concrete was stronger and more energy-absorbing under impact loading, than under static loading. [ABSTRACT FROM AUTHOR]

In this study, rubberized concrete samples were prepared by partial substitution (5 %, 10 % and 20 % replacements by volume) of sand by waste crumb rubber, and tested under impact three-point bending load, as well as static load. Three types of specimens (size 50 × 100 × 500 mm) namely, plain concrete, rubberized concrete, and double layer concrete (with rubberized concrete top and plain concrete bottom) were loaded to failure in a drop-weight impact machine by subjecting to 20 N weight from a height of 300 mm, and another three similar specimens were used for the static load test. In both the tests, the load-displacement and fracture energy of each specimen were investigated. Finite-element simulations were also performed to study the dynamic behaviors of the samples, by using LUSAS V.14 software. It was noticed that, the impact tup, and inertial and bending loads increased with the increase in the percentage of sand replacement by crumb rubber. It was interesting to observe that these effects were more significant in the double layer specimen compared to the plain and rubberized concrete samples. The static peak bending load always decreased with increase of rubber in the mix. In general, the strength and energy absorbing capability of rubberized concrete was better under impact loading than under static loading. The simulated load against displacement behaviors of all the samples were validated by the experimental results. [ABSTRACT FROM AUTHOR]

In this study, the effect of reducing cement by proportional addition of waste powder rubber on the performance of concrete under impact three-point bending loading were investigated experimentally and numerically. Concrete specimens were prepared by adding 5%, 10% and 20 % of rubber powder as filler to the mix and decreasing the same percentage of cement. For each case, three beams of 50 mm × 100 mm × 500mm were loaded to failure in a drop-weight impact machine by subjecting them to 20 N weight from 300mm height, while another three similar beams were tested under static load. The bending load-displacement behavior was analyzed for the plain and rubberized specimens, under static and impact loads. A three dimensional finite-element method simulation was also performed by using LUSAS V. 14 in order to study the impact load-displacement behavior, and the predictions were validated with the experimental results. It was observed mat, despite decreasing the cement content, the proportional addition of powder rubber until 10% could yield enhancements in impact tup, inertial load and bending load. [ABSTRACT FROM AUTHOR]

The establishment of a cement concrete dielectric constant model is the basic and key technique for applying the electromagnetic wave technology to concrete structure quality testing and internal damage detection. Based on the characteristics of the cement concrete, a new dielectric constant model is developed in theory after the linear model, the root-mean square model, and Rayleigh model are analyzed comprehensively. Dielectric constants of cement concrete are measured using hardware to evaluate components and circuits for frequency ranges. The theoretical analyses and experimental studies show the proposed model precision is highest and most suitable to interpret cement concrete dielectric properties when compared with the other three models. [ABSTRACT FROM AUTHOR]

An aggregate generation and packing algorithm based on Monte-Carlo method is developed to express the aggregate random distribution in cement concrete. A mesoscale model is proposed on the basis of the algorithm. In this model, the concrete consists of three parts, namely coarse aggregate, cement matrix and the interfacial transition zone (ITZ) between them. To verify the proposed model, a three-point bending beam test was performed and a series of two-dimensional mesoscale concrete models were generated for crack behavior investigation. The results indicate that the numerical model proposed in this study is helpful in modeling crack behavior of concrete, and that treating concrete as heterogeneous material is very important in fracture modeling. [ABSTRACT FROM AUTHOR]

This paper presents quantitatively the results of an experimental investigation on influence of mineral admixtures and superplasticizers on Vickers micro hardness (HV) of aggregate-paste interface in cement concrete. The HV was measured by Vickers hardness testing equipment. The results indicate that addition of fly ash decreases HV of the concrete. Although it decreases with the increase of ground granulated blast furnace slag (GGBS) replacement, the HV is higher than that of concrete containing fly ash at all replacements. The flying ash and GGBS composition increases HV in later curing ages, but does not improve it in early curing ages. Aminosulfonic acid based superplasticizer and aliphatic hydroxy sulphonate condensate superplasticizer can enhance HV in early curing ages. The HV of concrete with polycarboxylic acid superplasticizer is higher in later curing ages. [ABSTRACT FROM AUTHOR]

Effects of partial replacements of sand by waste crumb rubber and fine rubber, and cement by powder rubber, on the performance of concrete under low velocity impact loading were investigated. Specimens were prepared for 5%, 10% and 20% replacements by volume for both sand and cement. For each case, six beams of 100 mm × 100 mm × 500 mm were subjected to 5.15 kg hammer from 900 mm height. The number of blows of the hammer required to induce the first visible crack and ultimate failure of the beam were recorded. The results are presented in terms of impact energy required for the first crack and ultimate failure. The crumb and fine crumb rubbers increased the impact energy for both first crack and ultimate failure; the increase of impact resistance by crumb rubber was more than that by fine crumb rubber. However, the impact energy for both first crack and ultimate failure increased by the replacement of sand with fine crumb and crumb rubbers until 20%, while this energy increased with cement replacement by powder rubber until 10% replacements and then decreased, but is still higher than that of plain concrete. [ABSTRACT FROM AUTHOR]

A mathematical model is presented to simulate sulfate ion migration in cement concrete that was subjected to the coupled action from sodium sulfate solution and alternating stresses. The crack factor was derived based on the model of the concrete's response to external sulfate solutions through revised methods, such as diffusion path division and crack homogenization. A formula for effective diffusion (coefficient Dt), which is used to characterize the effect of alternating stresses on the sulfate ion diffusion, was proposed. The research uses Fick's second law for the diffusion of sulfate ions. A solution to the diffusion equation was proposed to determine the sulfate concentration under corrosion fatigue as a function of time and space. The sulfate concentration responses were obtained and compared with a variety of available data. Model simulations indicate a reasonable agreement with experimental data available in the literature [ABSTRACT FROM AUTHOR]

In this study, the influences of partial replacements of sand by fine crumb and crumb rubber particles, and cement by powder rubber, on the fracture characteristics of concrete were investigated experimentally. Specimens were prepared for 5%, 10% and 20% replacements by volume, for both sand and cement. Each case had three unnotched and notched specimens of size 600 mm × 75 mm × 150 mm; notches were 50 mm and 75 mm deep. The specimens were subjected to three points bending test in a computer-aided universal testing machine, and the fracture characteristics such as GIC, CMOD and Gf were analyzed. It was observed that, in all proportions, the replacement of sand by fine crumb and crumb rubber increased the fracture properties; the increase of fracture properties by crumb rubber was more than that by fine crumb rubber. However the cement replacement by powdered rubber could improve the fracture factors, only for 5% and 10% replacements. [ABSTRACT FROM PUBLISHER]

Municipal solid waste incinerator (MSWI) fly ash was melted into slag and then pulverized to generate particle sizes of less than 38 mμ in diameter (sieve #400) for experimental studies. Several slag-blended cement concrete (SBCC) specimens 10 cm in diameter and 20 cm in height were molded using 20% cement replacement with slag powder. Then, three water/cementitious (w/c) ratios, namely 0.36, 0.52 and 0.68, were selected to test the specimens for slump, setting time, compressive strength and durability. The compressive strengths of specimens of various ages were compared with those of ordinary Portland cement concrete (OPCC) specimens. The results reveal that the compressive strengths of the SBCC specimens were lower than those of the OPCC specimens at an early stage and became similar to those of the OPCC specimens at the age of 28 days. Moreover, the compressive strengths of the SPCC specimens are 100-113% and 105-118% those of the OPCC specimens after 56 and 90 days, respectively. The slumps (i.e. workability) and setting times for both the SBCC and OPCC specimens were similar. Our test results show that MSWI slag-blended cement concrete is usable for practical applications and can be applied to the concrete pavement. [ABSTRACT FROM AUTHOR]

Rehabilitation (restoration) of cement concrete pavements raises a number of problems for road engineers because of the rigidity of the structure. Solutions used generally fall into two categories: one which implies milling the concrete tiles (recycling them) and another solution which involves covering the existing pavement with asphalt road systems that behave well under traffic. This article aims to provide a multi-criteria analysis method regarding the choice of intervention in such sectors. The analysis will take into account three elements: - the cost - the degree of pollution of the technology that will be used - the duration of execution Each criterion will be graded according to an established algorithm and a ranking of the possible solutions will be made, based on this score [ABSTRACT FROM AUTHOR]

This study identifies the emission sources of various types of airborne organic compounds, which deteriorate cement concrete by penetrating into the concrete together with moisture. The study used high-performance liquid chromatography and gas chromatograph mass spectrometry. The results show that the types of organic compounds contained in decalcified cement concrete were very similar to those found in the total suspended compounds in the air, and that the source of the emissions was particles of exhaust from diesel vehicles and radial tires used in summer. Such organic compounds include substances suspected of having endocrine disrupting properties. Hydrolysis occurs when these substances penetrate into highly alkaline cement concrete, and leads to deterioration of the cement concrete and the release of alcohols and ammonia gases which pollute indoor air and may be a cause of the sick building syndrome. [Copyright &y& Elsevier]

Abstract: This paper reports results of a study conducted to assess the properties of cement kiln dust (CKD) blended cement concretes. Cement concrete specimens were prepared with 0%, 5%, 10%, and 15% CKD, replacing ASTM C 150 Type I and Type V. The mechanical properties of CKD concrete specimens were evaluated by measuring compressive strength and drying shrinkage while the durability characteristics were assessed by evaluating chloride permeability and electrical resistivity. The compressive strength of concrete specimens decreased with the quantity of CKD. However, there was no significant difference in the compressive strength of 0 and 5% CKD cement concretes. A similar trend was noted in the drying shrinkage strain. The chloride permeability increased and the electrical resistivity decreased due to the incorporation of CKD. The performance of concrete with 5% CKD was almost similar to that of concrete without CKD. Therefore, it is suggested to limit the amount of CKD in concrete to 5% since the chloride permeability and electrical resistivity data indicated that the chances of reinforcement corrosion would increase with 10% and 15% CKD. [Copyright &y& Elsevier]

The aim of this research was to find the best alternative for river sand in concrete. In both geopolymer concrete (GPC) and cement concrete (CC), the fine aggregates are replaced with various sustainable mineral ashes, and mechanical and durability tests are conducted. Specimens for tests were made of M40 grade GPC and CC, with five different soil types as river sand substitute. The materials chosen to replace the river sand are manufactured sand (M-sand), sea sand, copper slag, quarry dust, and limestone sand as 25%, 50%, 75%, and 100%, respectively by weight. GPF50 and CC50 were kept as control mixes for GPC and CC, respectively. The test results of respective concretes are compared with the control mix results. From compressive strength results, M-sand as a fine aggregate had an increase in strength in every replacement level of GPC and CC. Additionally, copper slag is identified with a significant strength reduction in GPC and CC after 25% replacement. Copper slag, quarry dust, and limestone sand in GPC and CC resulted in considerable loss of strength in all replacement levels except for 25% replacement. The cost of GPC and CC is mixed with the selected fine aggregate replacement materials which arrived. Durability and cost analyses are performed for the advisable mixes and control mixes to have a comparison. Durability tests, namely, water absorption and acid tests and water permeability and thermal tests are conducted and discussed. Durability results also indicate a positive signal to mixes with M-sand. The advisable replacement of river sand with each alternative is discussed. [ABSTRACT FROM AUTHOR]

In this paper, a new micromechanical framework to characterize the microstructural integrity and predict the effective properties of multi-phase particulate composites is presented. Within the framework, a new scalar micromechanical parameter is identified and used to derive new expressions for the effective elastic properties of particulate composites using the mean-field homogenization technique. The derived equations are then generalized for composites with multiple phase constituents. The generality of the proposed framework is demonstrated by combining the derived equations with the existing homogenization techniques such as the Mori–Tanaka method and the Generalized Maxwell's Approach (GMA). The results show that the theory delivers consistent estimates of the effective properties of two-phase elastic composite materials. The new scalar micromechanical parameter is also used to characterize the microstructural integrity of both asphalt mixtures and Portland cement concrete. The results show that the new scalar micromechanical parameter correlates well with multiple key fundamental properties of asphalt concrete mixture, including the creep rate, the fracture energy density, the endurance limit, and the damage rate parameters. The results also show that the new micromechanical framework can be used to accurately predict the effective modulus properties of Portland cement concrete mixtures. • A new framework for characterizing the microstructural integrity of composites. • Microstructural integrity characterized using the Composite Integrity Scalar (CIS). • Framework accounts for the effect of the aggregate shape and stiffness contrast. • Very accurate prediction of effective properties of Portland cement concrete. • CIS is well correlated to creep and fracture properties of asphalt mixtures. [ABSTRACT FROM AUTHOR]

• The expansive model of ITZ under dry-wet cycles and sulfate erosion was established. • The mechanical properties evolution of ITZ under sulfate erosion was calculated. • The cohesive force had the largest influence on the internal stress of concrete. • The plastic zone width and final expansion internal stress of ITZ were affected by water-cement ratio. Interfacial transition zone (ITZ) is of paramount importance to the durability of concrete. However, the evolution of damage characteristics and mechanical properties of ITZ under dry-wet cycles and sulfate erosion were not fully investigated in the literature. Therefore, this paper presents the expansive model of ITZ based on cylindrical cavity expansion theory, following by calculation of mechanical properties evolution of ITZ under sulfate erosion. The expansion ratio, Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD) were utilized to analyze the internal erosion and expansion characteristics of concrete with the water-cement ratio (w/c) of 0.3, 0.4 and 0.5. The results indicate that the expansion ratio of concrete increases with the erosion age and w/c. The new diffraction peaks appear in the XRD pattern after sulfate erosion. As compared with Poisson's ratio (γ) and internal friction angle (φ), cohesive force (C) has the largest influence on the internal stress and plastic zone width. The final internal stress and plastic zone width are affected by w/c, and the damage degree of concrete with 0.4 w/c is the minimum. This study provides new insights into damage mechanism of concrete and ITZ under dry-wet cycles and sulfate erosion, the results of which provide new perspectives for improving the durability of concrete. [ABSTRACT FROM AUTHOR]

The effects of structure parameters, such as molecular structure, segment kinds, molecular weight, and organic functional groups, on the performance of polyacrylic acid superplasticizer were discussed. According to the differences of chain sections, functional groups, etc, polyacrylic acid superplasticizer could be divided into A, B, C three parts. Among them, A chain section included sulfonic acid groups, B chain section carboxyl groups, C chain section polyester. Polyacrylic acid superplasticizers with different matching of A, B, C chain sections, different length of C chain section and different molecular weights were synthesized by acrylic acid, polyethylene glycol, sodium methyl allylsulfonate; the relation between the molecular structure and performance was also studied. The expetimental results indicate that the water-reduction ratio increases obviously with the increment of the proportion of sodium methyl allylsulfonate chain section in the molecular; the slump retention increases greatly with the increment of the proportion of acrylic acid chain section; the dispersion of cement particles increases with the increment of the chain length of polyethylene glycol; when the molecular weight is in the range of 5000, the dispersion and slump retentibity increase with the increment of the average molecular weight of polymers. [ABSTRACT FROM AUTHOR]

Abstract: Disposal of sludge of lime treated spent liquor pickling unit, as per the Act of Hazardous Waste (Management and Handling) Rules, 1989 is not easy. Its transportation and construction of lined disposal sites pose very severe problem. In the normal practice, sludge is being disposed off on sides of roads and railway tracks to generally fill the low-lying areas. This may cause severe health hazards. An attempt has therefore been made to utilize the treated spent liquor sludge in cement concrete. Design mix M20 has been prepared with varying concentration of sludge in the laboratory. Toxicity characteristics leaching procedure (TCLP) test as per USEPA has been carried out on cement concrete cubes. [Copyright &y& Elsevier]

Calcined clay (CC) is a promising pozzolan recently attracting research attention globally. Various investigations have shown the desirable attributes of the material as a Supplementary Cementitious Material (SCM) in cement concrete systems. This paper captures the compressive strengths impact of calcined clay-Portland cement (CC-PC) as binders in both concrete and soil systems. Grade 20 concrete cubes were prepared and tested; adopting five CC-PC binder blends obtained by replacing PC with CC at 0(control), 5, 10, 15, and 20%; designated as PC100, PC95, PC90, PC85, and PC80, respectively. Similarly, four CC-PC binder blends PC100(control), PC75, PC50, and PC25 were adopted to stabilise samples of A-2-6 lateritic soils at increasing content of 0, 2.5, 5, 7.5, 10% of the soil's weight. Results show that compressive strengths of the concrete samples increase with cement replacement. PC80 impacts the highest strengths with 7, 28 and 56-day strength activity indices (SAIs) of 174.7, 126.0 and 144.9%, respectively. In soil stabilisation, unconfined compressive strength (UCS) of the soil was found to increase with binder contents (2.5% to 10%) for the four binder designations. Compared to control (PC100), the PC75, and PC50 binders were better stabilisers with 7 and 28-day SAIs ranging between 105 and 275%, respectively. From the results, for applications across concrete and soil stabilisation works, CC has been shown to be a potential supplementary material for mitigating carbon emission without compromising on strength enhancement. [ABSTRACT FROM AUTHOR]

Deterioration of cement concrete specimens caused by simulated acid rain was investigated by laboratory tests. Before and after cement concrete specimens were exposed to simulated acid rain, the neutralized depth, the compressive strength and the chemical compositions in the hardened cement paste were measured. The mineralogical composition of the concrete specimens was analyzed with XRD. The results lead to the following conclusions: the neutralized depth of the concrete specimens of all experiments can be described as a power function of exposure duration, CaO loss and the reduction rate of strength increased with H+ and decreased with SO42- concentration in simulated acid rain. The original mineral compounds such as [Na K]AlSi3O8 and [Ca Na][SiAl]4O8 in the hardened cement paste are converted to CaSO4·2H2O, CaAl2Si2O8 and Ca3Al6O12·CaSO4. And these are larger in volume so that the reaction with SO42- ions result in volume expansion and strength decrease. The reduction rate of strength has a binary linear relation to the CaO loss rate and the ratio of SO3 content to CaO content in the hardened cement paste. So the deterioration of acid rain on the concrete specimen is caused by both H+ dissolution and SO42- expansion. [Copyright &y& Elsevier]

The workability, mechanical and physical properties are investigated, based on the requirements of the high properties of polymer cement concrete (PCC). The research results reveal that PCC is greatly improved and strengthened by adding appropriate polymer. At polymer/cement=0–0.15, its porosity decreases greatly due to the improved pore structure. The weak area at interface is strengthened. The workability, mechanical and physical properties are obviously enhanced with the proportion of polymer and cement. At the same time the properties are much improved under the adequate curing conditions and admixture (0–10%). [ABSTRACT FROM AUTHOR]

An experimental investigation was undertaken to study the potential use of Jordanian oil shale ash (OSA) as a raw material or an additive to Portland cement mortar and concrete. Different series of mortar and concrete mixtures were prepared at different water to binder ratios, and different OSA replacements of cement and/or sand. The compressive strength of mortar and concrete specimens, cured in water at 23 °C, was determined over different curing periods which ranged from 3 to 90 days. The results of these tests were subjected to a statistical analysis. Equations were developed by regression analysis techniques to relate the effect of batch constituents on the strength developments of OSA mortars and concretes. The models were checked for accuracy by comparing their predictions with actual test results.The obtained results indicated that OSA replacement of cement, sand or both by about 10% (by wt) would yield the optimum compressive strength, and that its replacement of cement by up to 30% would not reduce its compressive strength, significantly. It was found that OSA on its own possesses a limited cementitious value and that its contribution to mortar or concrete comes through its involvement in the pozzolanic reactions. The statistical model developed showed an excellent predictability of the compressive strength for mortar and concrete mixes. [Copyright &y& Elsevier]

• The calcium aluminates were fabricated on mortar substrates using (Ca-Al)-EDTA solutions, followed by high-heat treatment with a H2-O2 coupled flame. • The permeability was reportedly improved compared with the mortar itself. • The pore distributions in the mortar was changed, and shifted to smaller pore sizes. • A sealing process model combining metal-EDTA complex solutions and high-heat treatment was comprehensively proposed. Near-surface voids on a cement concrete sample were successfully sealed by applying a metal-ethylenediaminetetraacetic (EDTA) acid complex solution, followed by treatment with high-heat hydrogen/oxygen (H 2 -O 2) coupled flame. The calcium aluminates used for sealing were fabricated on cement substrates using calcium-aluminate (Ca,Al)-EDTA solutions prepared at various elemental ratios. The sealing effects were investigated through crystal & pore structure analysis and water permeability tests, using X-ray computed tomography (X-CT). Existence of the calcium aluminates were confirmed. From X-CT analysis, the average void diameter was changed from 16 μm to 10 μm with the calcium aluminate's sealing. A sealing process model combining metal-EDTA complex solutions and high-heat treatment, intended for the surface sealing of cement concretes used in construction, was comprehensively proposed. [ABSTRACT FROM AUTHOR]

• A novel pervious oyster shell habitat concrete is developed. • Cementitious materials, sand content, and paste volume all contribute to increased strength. • Carbonation to almost neutral pH occurs at 64 days, with significant carbonation at 28 days. • The developed module for oyster reef restoration is superior in weight, void space, demand for cement and natural aggregate, and carbon footprint. This study investigated the development of a more durable and sustainable cementitious composite substrate for oyster reef restoration using recycled oyster shells and low cement content. The effects of concrete mix proportions (w/c ratio, sand content, and cement content) on the physical properties of the hardened concretes were investigated. Increasing the water, sand, cement, and high-range water reducing admixture content improved both the compressive and flexural strength mostly by improving the coating of cementitious materials around the shells. The proposed material for reef restoration is superior in terms of cost, durability, environmental benefits, and carbon footprint. [ABSTRACT FROM AUTHOR]

[Display omitted] • The use of fiber or both silica fume and fiber improves concrete performance. • Steel fiber are superior to polypropylene fiber. • The use of silica fume and fiber allows to reduce the thickness of slab. • Concrete with 25.2 kg/m3 silica fume and 49.5 kg/m3 steel fiber showed best results. The main objective of this research is to develop high-strength concrete mixture (compressive strength ≥ 41 MPa) that is resistant to fatigue and suitable to produce slabs for modular pavements also known as precast concrete pavements. In addition to this, other characteristics (compressive strength, flexural strength and indirect tensile strength) were determined as well and the effect of fibers depending on type and amount in the presence and absence of silica fume has been revealed. Silica fume (0% and 7% by cement mass) and three types of fibers (one type of steel fibers and two types of polypropylene fibers) with three different amount of each fiber type were used to produce concrete mixtures. At all, 20 concrete mixtures were produced and tested in terms of static and cyclic bending, static compression and static tension. The research showed that the use of both fibers and silica fume in the concrete mixture leads to the best performance and steel fibers are superior to polypropylene fibers. Concrete mixture with 49.5 kg/m3 of steel fibers and 7% of silica fume by cement mass had compressive strength of 61 MPa and the highest resistance to fatigue and thus is the most potential to produce slabs for modular pavements. [ABSTRACT FROM AUTHOR]

• The interfacial properties of polymer and concrete was investigated by a newly designed apparatus. • A series of monotonic, cyclic and post-cyclic direct shear tests were carried out. • The effect of vertical stress shear rata, cycle number on interface characteristics were studied. The safety performance of geotechnical engineering is obviously affected by the interface characteristics of geotechnical materials. With widely use of the polymer in geotechnical engineering, the investigation for interface characteristics of polymer and concrete structure is necessary. In this paper, to investigate the interfacial shear properties of non-water reacted polymer and cement concrete, a series of displacement controlled monotonic direct shear (MDS) tests, cyclic direct shear tests (CDS) and post cyclic direct shear (PCDS) tests were carried out by using a newly designed direct shear test apparatus. The compressive strength of the polymer and cement concrete blocks are 2 MPa and 20 MPa respectively. The effects of vertical stress (50 kPa, 100 kPa, 150 kPa, 200 kPa), shear rate (1 mm/min, 2 mm/min, 3 mm/min, 4 mm/min and 5 mm/min), and cycle number on the investigated interface characteristics were studied. The results show that, with the increase of the vertical stress, the average peak shear stress of the interface gradually increases. As the vertical stress increase from 50 kPa to 200 kPa, the average peak shear stress increased by more than two times under various conditions. While with the increase of the shear rate, the average peak shear stress of the interface gradually decreases, but the reduction is small. And the reductions are all not more than 10% when the shear rate increases from 1 mm/min to 5 mm/min under all conditions; with the increase of the number of cycles, the average peak shear stress of the interface gradually decreases, and the decrease rate gradually decreases. When the vertical stress is 100 kPa and the shear rate is 3 mm/min, the average peak shear stress is reduced by 4.4% as the number of cycles increases from 1 to 5, while that is reduced by 1.2% as the number of cycles increases from 5 to 10; Under the given shear rate and vertical stress, the interface between polymer and cement concrete shows the shear softening in both MDS test and PCDS test. However, under the same vertical stress and shear rate, the shear strength and shear modulus of the MDS tests are greater than those of the PCDS tests. While the differences for MDS and PCDS are almost all not more than 5 kPa; with the increase of vertical stress, the shear strength and shear modulus of MDS test and PCDS test increase gradually. The shear strength increased by more than two times and the shear modulus increased by more than one times as the vertical stress increases from 50 kPa to 200 kPa. The shear strength is reduced by not more than 6% and the shear modulus is reduced by not more than 11% as the shear rates increase from 1 mm/min to 5 mm/min. The apparent cohesions are obviously influenced by cyclic direct shear, while the effective friction angles are a little influenced by CDS. [ABSTRACT FROM AUTHOR]

The authors of the article assessed the impact of operating fluids used to service aircraft on changing mechanical parameters of cement concrete intended for airport pavement. The research concerned concrete designed with the use of CEM I 42.5N LH NA low-alkali cement, broken granite aggregate, fine washed aggregate, and admixtures. The analysis included the assessment of changes in differences in endurance parameters over various research periods of up to 140 days. The obtained results allowed to carry out statistical analysis using the student's T-test. Research has shown a significant impact of operational fluids used in aircraft on the surface concrete properties of the airport. A reduction in the compressive strength of concrete exposed to one of the tested operating liquid to a reduction of 7.2% was observed over a period of 140 days, while there was no significant impact of operating fluids on tensile strength at splitting. [ABSTRACT FROM AUTHOR]