Low Strength Material Research Articles

Pervious concrete, plastic concrete and controlled low strength material- a special applications concrete

The paper presents the study carried out for three special concretes like Pervious Concrete, Plastic Concrete and Controlled Low Strength Materials (CLSM) using locally available materials. Pervious concrete is a concrete with high porosity. It is used in a wide range of applications including pervious pavements and helps in improving pavement skid resistance and reducing hydroplaning. This concrete was designed to meet the requirement of 28-day compressive strength of 10 MPa and water permeability of 0.50 cm/sec. Plastic concrete has low compressive strength but higher ductility and lower permeability. It is used for creating an impermeable barrier (cut-off wall) for containment of contaminated sites or seepage control in highly permeable dam foundations. This concrete was designed to meet the requirement of 28-day unconfined compressive strength of 1.5 to 2.5 MPa and confined compressive strength of 2.5 to 3.5 Mpa at confining pressure of 4 Kg/cm2. Controlled Low Strength Material (CLSM) or flowable fill mixtures are typically specified and used in place of compacted fill especially for backfill, utility bedding, void fill and bridge approaches. CLSM is a self-compacting, flowable, low strength cementitious material which suits the requirement of different applications such as excavatable backfill and structural backfill. The properties of CLSM that were investigated included bleeding, density of hardened CLSM, permeability and unconfined compressive strength at 7 days and 28 days age.

Tension and shear anchorage systems for limestone structures

Using anchorage systems to improve and repair existing buildings has been a favoured technique for many years. Whilst there has been an abundance of anchor performance analysis associated with anchorage into concrete, there has conversely been a comparative lack of investigation concerning the behavioural response of anchorage systems in low strength materials such as sedimentary stone. In the study reported herein, 78 adhesive anchors were subjected to tensile and shear testing in limestone blocks that were sourced from Oamaru, New Zealand. Three nominal anchor rod diameters (ɸ12, ɸ16, ɸ20mm) and two different bond agents (two-part epoxy adhesive, cement-based grout) were employed in the test regime. 54 anchors were installed to three varying depths of embedment described as a multiple of the anchor diameter (3ɸ, 5ɸ, 10ɸ), and were subjected to monotonic tension loading, and an additional 24 anchors were installed at one constant depth and subjected to a semi-cyclic shear loading regime. The results of these tension and shear experiments are summarised, with several anchor failure mechanism identified. Under tension, epoxy anchor behaviour was governed by the limestone strength, whereas grout anchor failure was governed by the bond strength. Anchor capacities in shear for epoxy and grout anchors were similar, however displacements were typically larger for grout anchors due to a low elastic modulus of grout. Also included is an investigation of the influence of moisture content on the strength properties of the limestone. In addition, a predictive equation for anchorage capacity within limestone is developed by applying analytical formulations originally conceived for anchorages installed into concrete, in order to study their applicability to weaker natural stone. The study provides a practicable baseline for future testing and the design of anchorage in sedimentary limestone. This dataset could be supplemented in future studies via investigations into alternative loading regimes, and/or the construction of limestone walls to investigate how local wall morphology impacts anchorage performance.

Preparation of novel Zn/Gr MMC using a modified electro-co-deposition method: Microstructural and tribo-mechanical properties

Zinc is a well-suited low-cost and widely alloyed metal used in several metal matrix composites (MMCs) due to its easy availability, low melting point, excellent thermal and electrical properties. However, Zn metal alone is a low strength material which restricts its applications mostly for alloying purpose. Inclusion of graphene nano-reinforcements in Zn metal matrix could result in high strength and cost-effective nanocomposite material. In this paper, impermeable graphene nano-reinforcements are encapsulated in Zn metal matrix using a modified electro-co-deposition method followed by powder metallurgy. The uniform distribution of nano-reinforcement of graphene layers across the Zn metal matrix was achieved. The prepared nanocomposite was characterized and tested to evaluate the microstructural, morphological and tribo-mechanical properties. The graphene content in Zn matrix decreased the crystallite size and imparted the advantageous grain strengthening effect. The graphene reinforced Zn MMC sample showed a significant enhancement in the mechanical and tribological properties than that of pure Zn sample.

Organic composite binder improving the physical and mechanical properties of low-strength stone materials

Based on the results of research and practical tests, the authors have developed a composition and proposed a technology for preparing an organic composite binder capable of deep penetration into pores of low-strength stone material with formation of a hydrophobic well-retained layer on its surface, which provides improvement of the main strength characteristics of the stone. Results of experimental studies are presented, optimal concentration of OCB and minimum processing time are determined. Practical recommendations are given for using the obtained strengthened material, which can act as a full-fledged independent working layer of road structure, as well as a component of asphalt concrete and cement concrete mixtures.

Research on Several Problems in the Characterization of Lightweight Cellular Materials by Low-Impedance Hopkinson Pressure Bar

Abstract There are great challenges in studying the dynamic mechanical behavior of lightweight cellular materials by using the traditional split Hopkinson pressure bar (SHPB) system because of the unique microstructure of such materials. To overcome these challenges, we present in this article a new experimental framework for dynamic loading tests of low-strength cellular materials from the elastic stage to the densification stage. Nylon is utilized as the compression bar in the SHPB system, and its low elastic modulus can cause larger displacement during dynamic loading. Meanwhile, polymethyl methacrylate (PMMA) inserts are attached to the bar end to prevent plastic deformation in that part, and a data correction method is employed to reduce the error caused by inserts. For the problem of wave dispersion during propagation in nylon bars, we use the in situ test method for dispersion correction to obtain more accurate results. We test a closed-cell aluminum foam by this modified SHPB test method and get ideal results. The test results of the aluminum foam show that its mechanical behavior is insensitive to the strain rate at the elastic stage and plastic collapse stage but sensitive to the strain rate at the beginning of the densification stage.

When low strength materials meet funicular structures: a sustainable clay floor structure solution for emerging contexts

The inevitable expansion of the built environment due to the rapid growth of the urban population in emerging contexts poses a great challenge for the sustainable development of local communities. This problem could be faced by providing adequate multistorey building solutions while using sustainable and eco-friendly materials, preferably from renewable or upcycled and locally available sources. These materials tend to have lower mechanical properties than those commonly used in conventional structures and therefore not adequate for elements subjected to bending such as floor slabs. This challenge can be met by improving the strength of the locally available materials and/or using geometries specifically designed to lower the structural stresses such as funicular structures. In this study, a novel clay-based cementless material is used. Different mixtures and additives were tested to achieve similar processing advantages as concrete. A parabolic arched floor element is designed based on a parametric analysis using graphic statics to reduce structural stresses and weight. The fabrication system is based on reusable formworks in which locally available earth is used as part of the mould. A four meters span arched floor is built to analyse its structural behaviour and to evaluate the proposed fabrication method.

Strength Characteristics of Controlled Low-Strength Materials with Waste Paper Sludge Ash (WPSA) for Prevention of Sewage Pipe Damage.

In this study, the effects of the mixing conditions of waste paper sludge ash (WPSA) on the strength and bearing capacity of controlled low-strength material (CLSM) were evaluated, and the optimal mixing conditions were used to evaluate the strength characteristics of CLSM with recyclable WPSA. The strength and bearing capacity of CLSM with WPSA were evaluated using unconfined compressive strength tests and plate bearing tests, respectively. The unconfined compressive strength test results show that the optimal mixing conditions for securing 0.8–1.2 MPa of target strength under 5% of cement content conditions can be obtained when both WPSA and fly ash are used. This is because WPSA and fly ash, which act as binders, have a significant impact on overall strength when the cement content is low. The bearing capacity of weathered soil increased from 550 to 575 kPa over time, and CLSM with WPSA increased significantly, from 560 to 730 kPa. This means that the bearing capacity of CLSM with WPSA was 2.0% higher than that of weathered soil immediately after construction; furthermore, it was 27% higher at 60 days of age. In addition, the allowable bearing capacity of CLSM corresponding to the optimal mixing conditions was evaluated, and it was found that this value increased by 30.4% until 60 days of age. This increase rate was 6.7 times larger than that of weathered soil (4.5%). Therefore, based on the allowable bearing capacity calculation results, CLSM with WPSA was applied as a sewage pipe backfill material. It was found that CLSM with WPSA performed better as backfill and was more stable than soil immediately after construction. The results of this study confirm that CLSM with WPSA can be utilized as sewage pipe backfill material.

Properties of bio-based controlled low strength materials

This study investigates the feasibility of enhancing construction materials sustainability using bio-based by-products as a partial replacement for natural sand. Controlled low strength material (CLSM) was selected as a practical application, thanks to its low strength requirements. The fine black spruce residual was added to different strength levels CLSM mixtures at rates 0%, 5%, 10%, and 20% as a partial replacement of natural sand. Fresh and hardened properties, including flowability, bleeding, density, compressive and tensile strengths, were evaluated. CLSM mixtures incorporating fine black spruce residuals were exposed to sulfate environment to examine their durability. The experimental results demonstrate that adding spruce-residuals had reduced the compressive strength; however, this reduction was within the acceptable limit. Moreover, results indicated that mixtures with high cement content could incorporate >20% spruce-residuals while maintaining adequate performance. The fine spruce-residuals have some filling effect and can reduce the pores leading to lower absorption rates. Dry/wet cycles will adversely affect the volume stability of CLSM, forming wide cracks that, in turn, accelerate degradation. Producing CLSM for farm applications is a feasible method for reusing such waste.

Using Dune Sand in Controlled Low-Strength Material for Backfilling: Field Installation and Numerical Simulation

The deflection of buried pipes depends on the exerted load and the embedment material. The portion of the exerted load transferred by the embedment material depends on the stiffness of the embedment material relative to that of the pipe. In the current study, four glass-reinforced polymer (GRP) pipes were buried in two different locations at the same depth under different geotechnical and installation conditions. For each of the test locations, two installation methods, namely controlled low-strength material (CLSM) and crushed rock, were used. The CLSM mixes were designed based on available native soil to satisfy the flow and strength criteria. Pipe deflection was meticulously measured at different stages of installation. In both cases, the behavior of the pipe showed the superior performance of CLSM as the backfill material. The behavior of the pipe was also evaluated by numerical modeling. The results of the numerical simulation were then compared with field test results, which showed a reasonable agreement. The pipe deflection was also predicted by a semiempirical equation and a numerical solution for the hardened CLSM. The effect of trench width on the vertical deformation was also evaluated through a parametric study.

Analysis of contact conditions and its influence on strain rate and temperature in friction stir welding

In friction stir welding (FSW), the real contact conditions between the tool and the workpiece and the range of strain rates experienced remain quite unclear. In this work, a coupled 3D thermo-mechanical numerical model was used to simulate the FSW process. A Parametric finite element analysis of the evolution of the contact conditions, strain rates and temperatures with the processing parameters, tool dimensions and base material plastic properties was conducted. The numerical model was able to capture the evolution of the mixed slipping/sticking contact conditions with the welding time and welding parameters. The temperature and strain rate gradients obtained in the numerical simulations were validated with experimental data, by calculating the grain size distribution, in the stirred volume, using the Zener-Hollomon parameter. Full sticking, full slipping and mixed slipping-sticking contact domains were identified in a process parameters chart. It was found that, meanwhile the temperature and the sticking fraction evolve in the same way with the processing parameters, the strain rate is mainly determined by the tool rotation speed, varying from an average of 68 to 324 s−1, when the tool rotation speed is increased from 300 to 1200 rpm. The contact conditions and the base material plastic properties were also found to mutually influence the material flow. In full sticking contact, high strength materials, with high strain rate sensitivity, may display a similar flow pattern to that of low strength materials. However, coarser and more uniform grain structures may result from the welding of high strength materials, as a result of the narrower range of strain rates experienced during welding combined with high heat input.

Development and application of a new similar material for fluid–solid coupling model test

Correct selection of similar materials is key to geomechanical model tests. According to similarity theories, a novel similar material for the fluid–solid coupling model test was developed to solve problems of low similarity and poor stability. A similar material is mixed with calcium carbonate, white cement, paraffin, quartz sand, silicone oil, talc, and iron powder. Quartz sand and talc powder are the main materials; white cement, calcium carbonate, and paraffin are glue; silicone oil and iron powder are regulators. The effects of different mixing ratios on the compressive strength, permeability coefficient, and specific gravity were studied using a single factor analysis method. The main components controlling the material properties were determined through numerous laboratory tests. The experimental results show that the new material strength is controlled by cement, paraffin, and calcium carbonate. Its permeability coefficient can be adjusted by altering the ratio of silicone oil and paraffin. Its specific gravity is mainly affected by iron powder. The new material can simulate low-strength and medium-strength rock materials with different permeabilities, and it can effectively solve the problem that mechanical properties and nonhydrophilic properties cannot be satisfied simultaneously. The material was successfully applied in geological model tests of fault water inrush.

Establishment of the Controlled Low-Strength Desulfurization Slag Prediction Model for Compressive Strength and Surface Resistivity

In this study, the desulfurization slag used the volume method to replace fine natural aggregates in controllable low-strength materials (CLSM); the desulfurization slag content (DS) and curing time (t) were used as variables to test the compressive strength and surface resistivity of CLSM and simulated a prediction model on the results. The test results showed during that the compressive strength on the 28th day, the average desulfurization slag replacement amount increased by 10%, and the compressive strength decreased by 0.9 MPa. The surface resistivity increases with age, and each ratio increases from seven days to 28 days, and the surface resistivity value increases from 9.3% to 20.6%. After that, a hyperbolic function and exponential function with multiple variables were used to establish a simulation model of the effects of the DS content and curing time on the compressive strength and surface resistivity of CLSM. Compared with the test results, the statistical analysis shows that the average absolute percentage error (MAPE) of the compressive strength is 9.17%, and the surface resistivity is 10.67%. From the results, the predictive analysis model developed in this paper provides good predictive results in terms of compressive strength and surface resistivity.

Thermal conductivity of steelmaking slag-based controlled low-strength materials over entire range of degree of saturation: A study for ground source heat pump systems

Controlled low-strength materials (CLSMs) with high workability and relatively high thermal conductivity can function as a thermal grout in the heat exchanger of ground source heat pump systems. The degree of saturation of CLSM strongly influences its thermal conductivity and thus affects the heat transfer capacity of the heat exchanger system. This study investigates the degree of saturation–thermal conductivity relationship of steelmaking slag-based CLSM using two sample preparation methods: a modified high-pressure membrane extractor coupled with a thermal needle probe (HP) and air-dried (AD) methods. The effect of grinding steelmaking slag on the mechanical properties and thermal conductivity of CLSM is also evaluated. The engineering properties test results indicate that ground steelmaking slag presents a positive effect on the compressive strength and thermal conductivity of CLSMs owing to the reduction of the inherent porosity and increased specific surface area of the raw steelmaking slag by the grinding. The degree of saturation and thermal conductivity have a linear relationship for both the AD and HP test methods. However, it was found that the AD method overestimates the thermal conductivity owing to the uneven distribution of the water content in the specimen. Finally, predictive equations are proposed to estimate the thermal conductivity of CLSM for the entire range of degree of saturation. Compared to the recently proposed equation, these equations are more appropriate for thermal conductivity estimation of grouting materials based CLSM, especially at low water content.

Experimental investigation on axially loaded adobe masonry columns confined by polymeric straps

Due to widespread applications of adobe masonry construction in rural areas of many seismic-prone countries, there is a high demand for conducting research on retrofitting of adobe buildings; however, such research is scarce. Among various structural aspects, confinement of an assemblage of adobe (i.e., unbaked clay brick) units and mud mortar is of primary concern in the current paper. To this aim, scaled adobe columns were wrapped by polypropylene (PP) straps, which are low-strength and low-cost polymeric materials, and were tested under uniaxial compression. The PP straps are placed at a certain interval while the two ends of a strap are joined together by a steel wire. No bonding agent is used between the straps and adobe surface. Three series of adobe columns with different aspect ratios of the cross section and different arrangements of adobe units in the cross section plan are examined and the experimental results in terms of axial stress versus axial strain, crack patterns, lateral strain variations, and tensile strain in the confining straps are reported. The comparison between the non-retrofitted adobe specimens and their confined counterparts revealed that the proposed retrofit technique by use of PP straps is highly efficient in improving the compressive strength and, more importantly, the ultimate axial strain of adobe columns. Besides, the retrofitted adobe specimens could maintain a considerable amount of post-peak residual strength up to large axial displacements. Finally, the experimental outcomes on the compressive strength are compared with predictions of an equation available in the literature.

Effectiveness of Textile Reinforced Mortar (TRM) materials for the repair of full-scale timbrel masonry cross vaults

This paper presents the experimental results obtained from tests on two masonry vaults reinforced by Textile Reinforced Mortar (TRM) materials subjected to monotonic and cyclic vertical settlements in one of their supports. Two full-scale square masonry timbrel vaults were built in one of ICITECH’s laboratories at the Universitat Politecnica de Valencia (Valencia, Spain) using the traditional Catalan layered-construction technique, with various layers of clay tiles arranged in two perpendicular masonry textures joined by lime and cement mortar joints. Due to their peculiar geometric and mechanical features, i.e. their high slenderness ratio, low tensile strength and high material heterogeneity, these structures are especially prone to damage from high-risk events such as soil settlement or seismic excitation. To evaluate their response to vertical support displacements, both vaults were pre-damaged by either vertical monotonic or cyclic settlements. They were then strengthened by a radial TRM strengthening configuration and re-tested until failure. A complex network of traditional and optical sensors was used to monitor displacements, deformation and the development of the cracking mechanism under both settlement conditions. The results obtained show that TRM materials can be used to effectively repair severely damaged masonry timbrel vaults, helping to partially restore the initial elastic stiffness, as well as doubling the vaults’ elastic phase and ultimate displacements. In addition, TRM materials did not alter the stiffness degradation trend, although they had a strong effect on peak reaction degradation and failure modes. This investigation represents a valuable and unique source of information about the efficacy of TRM materials to repair full-scale pre-damaged masonry timbrel vaults.

Development of Controlled Low-Strength Material Using Copper Mine Tailings

Development of Controlled Low-Strength Material Using Copper Mine Tailings

Numerical investigation on rigid and flexible pipelines embedded in granular and self-compacting materials

Self-compacting filling material or controlled low-strength material (CLSM) is a cementitious material which is liquid during filling, and it is used primarily as backfill, e.g., in trenches. Several products are currently used as CLSM such as flowable fill, controlled density fill, flowable mortar and low-strength plastic soil–cement. The low-strength requirement is necessary to allow for future excavation of CLSM. A two-dimensional numerical model was developed using the finite element system ABAQUS. In this model, the material behavior of granular soil and CLSM is described using an elasto-plastic constitutive model with Mohr–Coulomb failure criterion. Rigid and flexible pipes were modeled once embedded in sandy soil and once embedded in self-compacting material. The numerical model allows the modeling of the effect of hardening process on the overall behavior of the pipe–soil system. The main objective of this study is to investigate the behavior of rigid and flexible pipelines embedded in CLSM as a filling material numerically and to show advantages and disadvantages in comparison with the presently widely used filling materials like sand.

Prediction of superior target layer configuration of armour steel, mild steel and aluminium 7075-T651 alloy against 7.62 AP projectile

The ballistic performance of triple-layered in contact mild steel, Armox 500T steel and 7075-T651 Aluminum target plates have been studied at normal and oblique impact against 7.62 AP projectiles in order to understand the superior target configuration. The targets of layered configuration such as the high strength – low ductility (Armox 500T Steel), low strength – high ductility (Mild Steel) and medium strength – medium ductility (Aluminium 7075-T651 alloy) have been considered in the present study. The numerical results have been validated by the experiments reported in an earlier study in case of mild steel as well as Armox 500T steel whereas the 7075-T651 aluminium has been verified with the experimental results available in the literature. The Johnson-Cook elasto-viscoplastic material model calibrated by the authors for all three targets were employed in the numerical simulations. The close correlation between experimental and numerical results have been predicted. The superior target configuration has been identified from the simulation of eighteen target configurations as chosen from the present study. Further, the simulations were carried out on superior target layer configuration against varying oblique angle in order to identify the limiting velocity of projectiles and resistance of target. The results were presented in terms of stresses, residual velocity, deformations and the delamination of layers. It was concluded that the best configuration is the upper layer of low ductility – high strength material, middle layer of high ductility – low strength material and the lower layer of medium strength – medium ductility material. It was also observed that the projectile at oblique angle of maximum 35° perforates the superior layered target.

Metaheuristic algorithms in optimum design of reinforced concrete beam by investigating strength of concrete

The locations of structural members can be provided according to architectural projects in the design of reinforced concrete (RC) structures. The design of dimensions is the subject of civil engineering, and these designs are done according to the experience of the designer by considering the regulation suggestions, but these dimensions and the required reinforcement plan may not be optimum. For that reason, the dimensions and detailed reinforcement design of RC structures can be found by using optimization methods. To reach optimum results, metaheuristic algorithms can be used. In this study, several metaheuristic algorithms such as harmony search, bat algorithm and teaching learning-based optimization are used in the design of several RC beams for cost minimization. The optimum results are presented for different strength of concrete. The results show that using high strength material for high flexural moment capacity has lower cost than low stretch concrete since doubly reinforced design is not an optimum choice. The results prove that a definite metaheuristic algorithm cannot be proposed for the best optimum design of an engineering problem. According to the investigation of compressive strength of concrete, it can be said that a low strength material are optimum for low flexural moment, while a high strength material may be the optimum one by the increase of the flexural moment as expected.

The Effect of Lightweight Concrete Cores on the Thermal Performance of Vacuum Insulation Panels.

The performance of vacuum insulation panels (VIPs) is strongly affected by several factors, such as panel thickness, design, quality of vacuum, and material type. In particular, the core materials inside VIPs significantly influence their overall performance. Despite their superior insulation performance, VIPs are limited in their widespread use as structural materials, because of their low material strength and the relatively expensive core materials. As an alternative core material that can compensate these limitations, foamed concrete, a type of lightweight concrete with very low density, can be used. In this study, two different types of foamed concrete were used as VIP core materials, with their effects on the thermal behavior of the VIPs having been evaluated using experimental and numerical methods. To confirm and generate numerical models for VIP analysis, micro-computed tomography (micro-CT) was utilized. The obtained results show that insulation effects increase effectively when panels with lightweight concrete are in a vacuum, and both foamed concrete types can be effectively used as VIP core materials.