Prediction of combined effects of fibers and cement on the mechanical properties of sand using particle swarm optimization algorithm

In this research, a series of laboratory tests have been performed to investigate the effects of cement and polyvinyl alcohol (PVA) fiber on the performance of sand. Unconfined compression strength and compaction are also assessed in the present study. The cement contents were 0.5, 1, 2, 4, and 6% by weight of the dry sand. Fiber length and diameter were 12 and 0.1 mm, respectively, and were added at 0.0, 0.3, 0.6, and 1% by weight of dry sand. Finally, the obtained results from the experimental data with particle swarm optimization algorithm are used to generate a polynomial model for prediction unconfined compression strength, modulus of elasticity, and axial strain at peak strength. The results of the study indicate that the inclusion of PVA fiber increases the unconfined compressive strength and the peak axial strain. The elastic modulus of specimen decreased with increase in fibers. Maximum dry density of the sand–cement–fiber mixture increases with the increase in cement content and decreases with the increase in fiber content.     

Investigation of the deformability properties of fiber reinforced cemented sand

In this study, 72 consolidated drained triaxial tests have been carried out to evaluate the effect of relative density, weight ratio of fibers, weight ratio of cement and confining pressure on the deformability properties of specimens made from Babolsar sand, Portland cement type II and polyvinyl alcohol (PVA) fibers. The results of this study show that the stiffness corresponding to 50% of the shear strength increases with the addition of cement. The presence of fibers within the cement specimen reduces stiffness. On the other hand, for uncemented specimen, adding fibers can reduce the stiffness of the specimens by 80% density, while adding fibers increases stiffness for specimens with 50% density. Adding cement to sand increases the secant stiffness at lower strains, but at high strains, cement content does not affect the secant stiffness. For specimens with relative density of 80%, in low strains, adding fibers reduces the secant stiffness. In high strains, the presence of fibers increases the secant stiffness. The distance between the yielding point and failure point increases with increasing confining pressure and fiber content, but adding cement reduces this distance. The yielding point of cemented sample depends on cement content and confining pressure. The inclusion of PVA fibers to the cemented soil increases the energy absorption. The addition of cement increases the energy absorption, but the amount of energy absorption increase is not significant. Moreover, the increase of confining pressure increases the difference in the absorbed energy of the specimens with different relative densities.     

Predicting the stress-strain behaviour of zeolite-cemented sand based on the unconfined compression test using GMDH type neural network

Stabilizing sand with cement is considered to be one of the most cost-effective and useful methods of in-situ soil improvement, and the effectiveness is often assessed using unconfined compressive tests. In certain cases, zeolite and cement blends have been used; however, even though this is a fundamental issue that affects the settlement response of a soil, very few attempts have been made to assess the stress-strain behaviour of the improved soil. Also, the majority of previous studies that predicted the unconfined compressive strength (UCS) of zeolite cemented sand did not examine the effect of the soil improvement variables and strain concurrently. Therefore, in this paper, an initiative is taken to predict the relationships for the stress-strain behaviour of cemented and zeolite-cemented sand. The analysis is based on using the unconfined compression test results and Group Method of Data Handling (GMDH) type Neural Network (NN). To achieve this end, 216 stress-strain diagrams resulting from unconfined compression tests for different cement and zeolite contents, relative densities, and curing times are collected and modelled via GMDH type NN. In order to increase the accuracy of the predictions, the parameters associated with successive stress and strain increments are considered. The results show that the suggested two and three hidden layer models appropriately characterise the stress-strain variations to produce accurate results. Moreover, the UCS values derived from this method are much more accurate than those provided in previous approaches. Moreover, the UCS values derived from this method are much more accurate than those provided in previous approaches which simply proposed the UCS values based on the content of the chemical binders, compaction, and/or curing time, not considering the relationship between stress and strain. Finally, GMDH models can be considered to be a powerful method to determine the mechanical properties of a soil including the stress-strain relationships. The other novelty of the work is that the accuracy of the prediction of the strain-stress behaviour of zeolite-cement-sand samples using the GMDH models is much higher than that of the other models.     

A dimensional description of the unconfined compressive strength of artificially cemented fine-grained soils

Abstract

This study aims at establishing a universal predictive model for the unconfined compressive strength (UCS) of artificially cemented fine-grained soils. Model development, its validation and calibration were carried out using a comprehensive database gathered from the research literature. The dimensional analysis concept was successfully extended to the soil–cement UCS problem, thereby leading to a practical dimensional model capable of simulating the UCS as a function of the blend’s index properties — that is, cement content, specific surface area, curing time, and the compaction state parameters (including water content and dry density). The predictive capability of the proposed model was examined and further validated using routine statistical tests, as well as conventional fit-measure indices which resulted in R²?>?0.95 and NRMSE < 5%. A sensitivity analysis was also carried out to quantify the relative impacts of cement content, curing time and soil plasticity on the UCS. The higher the soil plasticity, the higher the positive sensitivity to cement content, implying that soils of higher plasticity would require higher cement contents for stabilization. On the contrary, the higher the soil plasticity, the lower the positive sensitivity to curing time, indicating a more effective cement hydration in soils of lower plasticity. Finally, an explicit calibration procedure, involving a total of three UCS measurements for three recommended soil–cement mix designs, was proposed and validated, thus allowing for the proposed model to be implemented with confidence for predictive purposes, preliminary design assessments and/or soil–cement optimization studies.     

Effects of silica fume on cemented sand using ultrasonic pulse velocity

When the geotechnical engineering projects have to be built on weak soils, problems related to bearing capacity and settlement arise. Chemical stabilization of soil using cement is a popular and effective technique that can significantly improve workability and shear strength of soil. However, very limited studies have been conducted to reveal the effect of silica fume on the engineering properties of cement-stabilized sandy soil. For this purpose, in the present study, a series of laboratory tests including standard Proctor compaction, unconfined compression and ultrasonic pulse velocity tests were carried out on sand-cement-silica fume samples. Moreover, it has been attempted to investigate the relation between ultrasonic pulse velocity and unconfined compressive strength of cemented sand containing silica fume. The cement contents were 3, 5 and 7% and silica fume contents were 0, 0.25, 0.5 and 1% by weight of dry sand. The cylindrical specimens were prepared and cured for 3, 7, 14, 28, 42 and 56?days and tested. The results show that inclusion of silica fume to cemented sand increases maximum dry unit weight, unconfined compressive strength and ultrasonic pulse velocity while decreases optimum moisture content. In addition, according to the obtained results, acceptable correlations exist between ultrasonic pulse velocity, unconfined compressive strength and stiffness.     

水泥改良弱胶结砂岩填料的性能研究

针对以弱胶结砂岩作为填料引起的路基病害问题,提出以水泥改良弱胶结砂岩的可行性,分别用水泥掺量为3％、4％、5％、6％、7％、8％、9％改良弱胶结砂,对改良试样进行击实试验、压缩试验、直剪试验、无侧限抗压强度试验、加州承载比等试验,得到水泥改良弱胶结砂岩作为路基填料是可行的,水泥掺量为6％时,改良填料的压缩性能,填料试样的抗剪强度、各龄期的无侧限抗压强度、承载能力等路用性能均大幅度增强,所以水泥掺量为6％对弱胶结砂岩的改良效果最为明显.     

Uniaxial compaction behaviour and elasticity of cohesive powders

The compression and compaction behaviour of bentonite, limestone and microcrystalline cellulose (MCC) — three cohesive powders widely used in industry were studied. Uniaxial compression was performed in a cylindrical die, 40 mm in diameter and 70 mm high, for three selected cohesive powder samples. The initial density, instantaneous density and tablet density were determined. The influence of maximum pressure and deformation rate was examined. The secant modulus of elasticity E_sec was calculated as a function of deformation rate v, maximum pressure p and powder sample. After compaction experiments in hydraulic press at three pressures - p = 30, 45 and 60 MPa - and two different deformation rates, the strength of the produced tablets was examined in a material strength testing machine.From uniaxial compression tests performed on the universal testing machine for loading and unloading, the modulus of elasticity E was calculated on the basis of the first linear phase of unloading. The total elastic recovery of tablets was also obtained.     

Effect of mechanical property of cemented soil under the different pH value

Cemented soil has been widely used in civil engineering. Groundwater affected by several environment factors, such as agriculture, industry, living and seawater, is often acid or alkaline and usually aggressive to cemented soil. In practice, unconfined compressive strength (UCS) is often used as one of the basic indicators to evaluate the mechanical property of cemented soil. This paper mainly studies the impacts of environmental contamination on the mechanical property of cemented soil, the factors such as cement content, curing age and pH value are taken into consideration. The results show that, the appearance of cemented soil is seriously eroded under acid conditions; while in alkaline conditions it is affected slightly. The UCS of cemented soil increases with cement content and curing age. However, the increase is much slower than that of regular cemented soil. In strong acid and strong alkaline environments, the strength loss can reach 30%. In addition, the electron scanner was used to observe the microstructure of test blocks, and microscopic mechanism of failure was analyzed. The results of this paper can provide reasonable basis for durability evaluation, residual life prediction and durability design of cemented soil.     

Fibre-reinforced lightweight engineered cementitious composites for 3D concrete printing

While the 3D printing technology for cementitious composites has developed rapidly, a combination of 3DP technology and lightweight engineered cementitious composites (LWECCs) could improve many aspects of the construction industry. In this study, a fibre-reinforced high-performance LWECC for extrusion-based printing was proposed. First, six LWECCs were prepared, incorporating two kinds of hollow glass microspheres (HGMs) in varying replacement ratios of fly ash (FA) at 60 wt%, 80 wt%, and 100 wt%. In addition, polyvinyl alcohol (PVA) fibre was introduced given its shrinkage resistance and improvement in printability performance. Thereafter, fresh property (slump loss and setting time), unconfined compression strength (UCS), and flexural strength experiments thoroughly investigated the optimised LWECC design, which was later calibrated for the printing procedure via a printability assessment, including extrudability and buildability. The UCS, flexural strength, and densities of the printed and cast specimens were compared. Lastly, a microstructural investigation using a scanning electron microscope described the reinforcement mechanism of PVA fibre upon the performance of the printed structures and HGMs. The addition of HGMs significantly improve the lightweight property that reaches a value at 1384 kg/m³ but inevitably negates mechanical properties. The printed LWECC obtains 33.6 MPa for UCS and 9.29 MPa for flexural strength. When the printed filament was perpendicular to loading direction, superior toughness was observed, creating a 63% and 40% increase for UCS and flexural strength, respectively.     

Triaxial behavior of fiber-reinforced cemented sand

In this research, a series of laboratory tests have been performed to investigate the effects of cement and polypropylene (PP) fiber on the triaxial behavior of sand. The cement contents were 0 and 5% by weight of the dry sand. Fiber length and diameter were 18 and 0.023 mm, respectively, were added at 0 and 0.6% by weight of dry sand–cement. Triaxial compression tests were performed at confining pressures of 0.1, 0.25, 0.5, and 1 MPa. The results of the study indicate that the inclusion of PP fiber increases the shear strength and the peak axial strain. The elastic modulus of specimen decreased with increase in fiber content and increased with the increase in cement content. Moreover, the initial stiffness and peak strength increased by increasing cement content.     

水泥锶渣混凝土路用性能评价

为了分析水泥锶渣混凝土用于低交通量道路路面的可行性,采用正交方法分析了水泥用量、用水量(坍落度)、砂率、碎石级配等因素对水泥锶渣混凝土抗压强度和抗折强度的影响规律,优选出合理的材料配合比;试验对不同水泥用量的水泥锶渣混凝土的力学性能、干缩性能、温缩性能和抗冻性能进行了系统评价.结果表明:水泥锶渣混凝土强度低于普通C30混凝土,但“折压比”高,弹性模量小,具有较好的抗裂性能;于缩系数比普通混凝土低20％,温缩系数为普通混凝土的53％,具有优良的抗收缩性能;抗冻性能低于普通混凝土;水泥锶渣混凝土可用于非冰冻地区低交通量道路路面.     

高性能橡胶粉混凝土动态压缩性能研究

在微机控制电液伺服压力试验机上对高性能橡胶粉混凝土(HPRC)试件进行单轴压缩试验,研究了橡胶粉体积掺量和应变率对高性能橡胶粉混凝土性能的影响.研究结果表明,高性能橡胶粉混凝土峰值应力和割线模量表现出一定的应变率强化效应,而橡胶粉的掺入会降低峰值应力和割线模量提升的幅度;峰值应变未表现出应变率敏感性,橡胶粉的掺入会增强混凝土的变形能力;分析了应变能与试件破坏形态的关系,应变率增大,试件破坏前贮存的应变能增大,试件破坏更严重,呈脆性破坏,掺入橡胶粉后,混凝土的韧性改善较大,试件破坏时呈现裂而不散的特性.     

Effect of stereoregularity and molecular weight on the mechanical properties of poly(vinyl alcohol) hydrogel

The effect of the stereoregularity and molecular weight of poly(vinyl alcohol) (PVA) on the mechanical properties of hydrogel was investigated. Compressive strength, creep behavior, and dynamic viscoelasticity were measured on hydrogels of syndiotacticity‐rich PVA derived from poly(vinyl pivalate) (D_p = 1690 diad‐syndiotacticity = 61%, D_p = 8020 diad‐syndiotacticity = 62%) and atactic PVA (D_p = 1750 diad‐syndiotacticity = 54%, D_p = 7780 diad‐syndiotacticity = 54%). Increasing the molecular weight of molecular chains constituting the gel improved the compressive strength of atactic PVA hydrogel. The stereoregularity of PVA had a greater effect than molecular weight on the strength of the hydrogel. Gel prepared from 8.8 g/dL syndiotacticity‐rich PVA had a high compressive modulus of 10 kPa, and the compressive modulus of the gel prepared from 3.3 g/dL was comparable with that of atactic PVA hydrogel prepared with more than 6 g/dL. The dynamic storage modulus of the gel derived from syndiotacticity‐rich PVA was remarkably higher than that of the atactic PVA gel and remained constant up to 60°C. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Modeling of compressive strength of cemented sandy soil

This paper attempted to show the application of particle swarm optimization in the prediction of the compressive strength of cement sandy soil from the curing period, porosity of sample and percentage of cement. The results of the study show that the unconfined compressive strength of the cement stabilized sandy soil increases with an increasing cement content curing time period. Moreover the compressive strength decreases with an increasing porosity. The compressive strength improvement due to cement treatment has a larger increase in samples with less porosity. In addition, particle swarm optimization algorithm is and accurate technique in estimation of compressive strength of cement stabilized sandy soil. In order to compare of existing correlations, a total number of 100 unconfined compressive tests and 15 scanning electron microscope tests have been conducted on cemented Babolsar sand. It can be concluded that compared to existing correlations models, particle swarm optimization algorithm models give more reliable prediction about compressive strength of cement satblized sandy soil. Moreover, the sensitivity analysis of the polynomial model shows that cement content and porosity have significant impact on predicting unconfined compressive strength.     

Effect of hydrostatic pressure on the deformation behavior of polyethylene and polycarbonate in tension and in compression

The stress-strain response of crystalline high density polyethylene and of amorphous polycarbonate has been determined in tension and in compression at superimposed pressures up to 1104 MPa(160 ksi). Strain softening occurred in the polycarbonate at low pressures but was inhibited by pressure. Tensile necking occurred in both materials, but was promoted by pressure in polyethylene and inhibited in polycarbonate. The initial modulus, E, and the flow stress, σ, at a given offset strain varied linearly with the mean pressure, P, with essentially the same pressure coefficient, α. Thus, E = (1+αP)E₀ and σ = (1+αP)σ₀, where E₀ and σ₀ are values at zero mean pressure. In polyethylene, the coefficient, σ₀, was the same in tension and compression, indicating that the strength differential between tension and compression was a simple manifestation of pressure-dependent yielding. In polycarbonate the coefficient, σ₀, was different in tension and in compression, implying an effect due to the third stress invariant or to anisotropy. The results suggest a constitutive model for polymers in which the flow stress is linearly dependent on mean pressure, but in which inelastic volume change is negligible. The results also suggest that the pressure dependence of flow stress in polymers is the same as that of the initial modulus.     

Replacement of raw mix in cement production by municipal solid waste incineration ash

The feasibility of municipal solid waste incineration (MSWI) ash utilized as the replacement of raw mix in cement production is investigated. Result shows that sieving, self-grinding, and magnet separation processes are necessary to remove the debris, salt, and metallic contents that existed in the MSWI ash. By using the pretreated MSWI ashes, the produced cement specimens were in compliance with the unconfined compression strength (UCS) standard in Taiwan at small replacement percentage (<5%). When ash replacement percentage is large (more than 10%), the strength development of specimens would be hindered due to the deficient formation of the calcium silicate. Calculation on lime saturation factor (LSF) also shows a descending trend in consequence of the increase in replacement percentage. Thus, compositional effect should be taken into consideration for promoting the calcium silicate formation at the case of large ash replacement. In this research, adjustment of chemical composition was achieved by adding 183 g calcium oxide per kilogram of cement raw mixture with 15% ash replacement. After adjustment, the produced cement could develop seven- and fivefold increase on UCS compared with those without calcium oxide supplement at 3 and 7 days of curing, respectively. Results concluded that the MSWI ash was suitable in reuse for cement production under a well-conditioned situation.     

超高含水率水泥固化泥炭土压缩模量和固结系数研究

泥炭土具有高含水率、高有机质含量、大孔隙比和低剪切强度等特点。化学固化常用于提升泥炭土地基承载力和抵抗变形能力。通过开展单向固结试验,研究了含水率、有机质含量、pH值、水泥掺量和掺料粒径对水泥固化泥炭土压缩模量和固结系数的影响。研究表明,随着水泥掺量和养护龄期增加,水泥水化反应生成的凝胶不断增长,固化土压缩模量随之增长。泥炭土初始含水率从600%降至300%后,固化土压缩模量增加了3.5倍。有机质含量从40%增至80%(质量分数)时,固化土压缩模量降低了50%。pH值从7.0降至3.5时,固化土压缩模量降低了15.8%。固化泥炭土的压缩模量和固结系数受含水率、水泥掺量影响最大,有机质含量次之,pH值影响最小。掺石英砂能提升固化泥炭土的压缩模量,且石英砂粒径越小,固化土压缩模量增幅越大。     

Dynamic properties of short fiber–EPDM matrix composites as a function of strain amplitude

The dynamic properties of composite materials consisting of an ethylene–propylene rubber matrix (EPDM) and short polyester polyethylene-terephthalate (PET) fiber vary with dynamic stress amplitude applied to the material. These variations support the statement that fiber treatment with 1,4-carboxy-sulphonyl-diazide, which acts as a bridge between the fiber and the matrix and hence enhances the strength of the interface enabling it to resist greater strain applied to the composite and, as a consequence, yielding greater retention values of the storage modulus, measured longitudinally to preferential fiber orientation, E′_L. By means of transversal measurements of the storage modulus, E′_T, of these materials it is possible to determine a parameter b, which eventually indicates the degree of matrix–fiber bonding and which is consistently higher for materials filled with surface-treated fiber. This enhanced phase adhesion is further confirmed by higher equivalent interfacial thickness values, ΔR, which, in addition, vary less with increasing dynamic strain amplitude. Finally dissipated energy variation or mechanical energy loss, E_loss, is studied as a function of fiber content and strain amplitude. Experimental findings show E_loss to increase with fiber content and strain amplitude, when measured at constant strain amplitude ?₀, and to yield higher values for treated fiber samples. © 1994 John Wiley & Sons, Inc.     

Effects of γ radiation on fiber‐reinforced polymer concrete

Composites were made from 30% unsaturated polyester resin + 70% calcium bentonite and marble as aggregates, as well as 0.3 and 0.4 vol% of nylon fibers. The fiber‐containing polymer concretes (PCs) were subjected to 5, 10, 50, and 100 kGy applied radiation doses. The compressive strength values depend on both the fiber concentration and the irradiation dose applied. Moreover, the polyester‐based PCs containing two mineral aggregates, calcium carbonate and marble, have lower compressive strength values than those reported earlier for PCs containing only either silica sand or CaCO₃. However, significant improvement of the compressive strain and the compression modulus of elasticity are achieved when nylon fibers are added. Both these properties go symbatically with the radiation dose. Mechanical characteristics can be related to the morphological features observed by scanning electron microscopy. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers