Effect of fiber reinforcement and distribution on unconfined compressive strength of fiber-reinforced cemented sand

A series of unconfined compression tests were carried out to examine the effect of fiber reinforcement and distribution on the strength of fiber-reinforced cemented sand (FRCS). Nakdong River sand, polyvinyl alcohol (PVA) fiber, cement and water were mixed and compacted into a cylindrical sample with five equal layers. PVA fibers were randomly distributed at a predetermined layer among the five compacted layers. The strength of the FRCS increases as the number of fiber inclusion layers increases. A fiber-reinforced specimen, where fibers were evenly distributed throughout the five layers, was twice as strong as a non-fiber-reinforced specimen. Using the same amount of fibers to reinforce two different specimens, a specimen with five fiber inclusion layers was 1.5 times stronger than a specimen with one fiber inclusion layer at the middle of the specimen. The fiber reinforcement and distribution throughout the entire specimen resulted in a significant increase in the strength of the FRCS.     

Modelling tensile/compressive strength ratio of artificially cemented clean sand

The present work proposes a new theoretical model for predicting both the splitting tensile strength (q_t) and the compressive strength (q_u) of artificially cemented sand and assesses their ratio for a given material. The proposed model is based on the concept of the superposition of the failure strength contributions of the sand and cement phases. The sand matrix obeys the concept of critical state soil mechanics, while the strength of the cemented phase can be described using the Drucker-Prager failure criterion. The analytical solutions are compared against the results of tests on three different types of cemented clean sand cured for different time periods. While the analytical relation fits the experimental data well, it also provides a theoretical basis for the explanation of some features related to the experimentally derived strength relationships for cemented clean sand. The value of the power relationship between the strength and the porosity/cement ratio index seems to be governed by the soil matrix properties, while the interdependency of the strength and the curing time can also be captured. For a given cemented sand, the model equally confirms the existence of a unique tensile/compressive strength ratio (q_t/q_u), independent of the curing time and primarily governed by the compressive to tensile strength ratio (or the friction properties) of the cement. It is also confirmed that the q_t/q_u ratio changes within a narrow range for different frictional properties of the cementing phase.     

建筑垃圾再生料无侧限抗压强度试验

为分析红砖建筑垃圾再生料在城市道路中应用的可靠性,加大砖渣建筑垃圾的再利用,在一定级配下,分别测试混凝土再生料与红砖再生料在五种不同比例混合的情况下制成试块的无侧限抗压强度值。结果表明:100%混凝土再生料与按照三种不同比例的混凝土与红砖再生料可以用在道路的基层中;100%红砖建筑垃圾再生料可以用作城市道路底基层中。     

Unconfined compressive strength of fly ash reinforced with jute geotextiles

A series of unconfined compressive strength (UCS) tests have been conducted on unreinforced fly ash as well as fly ash reinforced with jute geotextiles. The effects of different governing parameters viz., degree of saturation, size of samples, number of jute geotextile layers and age of sample on UCS have been studied. From the test results it is found that the values of UCS are maximum at degree of saturation of 70–75%. The effect of sample size on the values of UCS for unreinforced fly ash is insignificant, whereas with increase in diameter of sample, values of UCS increase in case of reinforced fly ash. With increase in number of jute geotextile layers for reinforced fly ash samples, values of UCS increase and maximum enhancement is found to be around 525% with 4 layers of reinforcement. A non-linear power model has been developed to estimate unconfined compressive strength (UCS_R) of fly ash reinforced with jute geotextiles in terms of unconfined compressive strength (UCS_UR) of unreinforced fly ash and number of layers of reinforcement (N).     

Unconfined compressive strength of loose sandy soils grouted with zeolite and cement

Cement production requires a lot of energy and is also one of the most important sources of carbon dioxide emissions. Consequently, the replacement of part of the cement with a more environmentally friendly material, such as zeolite, is of great importance. The present research involves the conducting of a series of laboratory tests on loose sand specimens ($D_r\approx 30\%$) grouted with cementitious materials (cement and zeolite) to investigate the effect of different parameters, such as the size of the sand particles, the ratio of water to cementitious materials (W/CM) and the replacement of a certain percentage of the cement in the grout with zeolite (Z), on the unconfined compressive strength (UCS) of the grouted sand specimens. The results indicate that for all the grout W/CM and sand grain sizes, when Z is increased from zero zeolite (Z₀), the UCS initially increases. Then, after reaching an optimal amount (Z₃₀), it decreases. Moreover, increasing both the size of the sand particles and the W/CM of the grout is seen to reduce the UCS of the grouted specimens. The UCS of the grouted sand specimens increases with the equilibrium of SiO₂ and Al₂O₃ with CaO elements in the grouting suspension. Finally, equations with a high performance are proposed to predict the UCS of sands grouted with zeolite-cement using a multiple regression model (MRM) and a group method of data handling (GMDH)-type neural network.     

A constitutive model for evaluation of mechanical behavior of fiber-reinforced cemented sand

The aim of this study is to present a constitutive model for prediction of the mechanical behavior of fiber-reinforced cemented sand. For this purpose, a generalized plasticity constitutive model of sandy soil is selected and the parameters of the model are determined for three types of sandy soils using the results of triaxial tests. Next, the proposed model is developed using the existing models based on the physico-mechanical characteristics of fiber-reinforced cemented sand. The elastic parameters, flow rule and hardening law of the base model are modified for fiber-reinforced cemented sand. To verify the proposed model, the predicted results are compared with those of triaxial tests performed on fiber-reinforced cemented sand. Finally, the efficiency of the proposed model is studied at different confining pressures, and cement and fiber contents.     

Enhancement of unconfined compressive strength of sand test pieces cemented with calcium phosphate compound by addition of various powders

To improve the unconfined compressive strength (UCS) of a novel chemical grout composed of a calcium phosphate compound (CPC-Chem), we performed UCS tests and scanning electron microscopy (SEM) observations on sand test pieces cemented with CPC-Chem and four kinds of powders (tricalcium phosphate, TCP; magnesium phosphate, MgP; calcium carbonate, CC and magnesium carbonate, MgC) as seed crystals. The UCS of the CPC-Chem test pieces cemented with TCP and CC was significantly greater than that of the test pieces with no added powders. The UCS of the test pieces with TCP and CC additives exceeded the targeted value of 100 kPa and increased to a maximum of 261.4 kPa and 209.7 kPa for the test pieces with TCP and CC additives, respectively. Furthermore, the UCS of test pieces with 1 wt% or 5 wt% TCP and 1 wt% CC additives was maintained at a level exceeding 200 kPa for 168 days. SEM observations revealed net-like and three-dimensional structures in segments of test pieces cemented with 1 wt% or 5 wt% TCP and 1 wt% CC in CPC-Chem, which could have been the reason of the long-term stability of UCS (over 200 kPa for 168 days) observed in this study. These results suggest that the addition of TCP and CC significantly enhances the ground improvement afforded by CPC-Chem.     

Comparative mechanical behaviors of four fiber-reinforced sand cemented by microbially induced carbonate precipitation

Bulletin of Engineering Geology and the Environment - Microbially induced carbonate precipitation (MICP) has been found promisingly to improve soil mass properties with the environmentally friendly...     

Modelling tensile/compressive strength ratio of fibre reinforced cemented soils

The present work proposes a theoretical model for predicting the splitting tensile strength (q_t) - unconfined compressive strength (q_u) ratio of artificially cemented fibre reinforced soils. The proposed developments are based on the concept of superposition of failure strength contributions of the soil, cement and fibres phases. The soil matrix obeys the critical state soil mechanics concept, while the strength of the cemented phase can be described using the Drucker-Prager failure criterion and fibres contribution to strength is related to the composite deformation. The proposed developments are challenged to simulate the experimental results for fibre reinforced cemented Botucatu residual soil, for 7 days of cure. While the proposed analytical relation fits well the experimental data for this material, it also provides a theoretical explanation for some features of the experimentally derived strength relationships for artificially fibre reinforced cemented clean sands. A parametric study to analyse the effect of adding different fibre contents and fibre properties is provided. The proposed modelling developments also confirm the existence of a rather constant q_t/q_u ratio with moulding density, cement and fibre contents .     

Fibre-reinforced cemented soils compressive and tensile strength assessment as a function of filament length

This study aims to develop a dosage methodology based on tensile and compressive strength for artificially cemented fibre reinforced soils considering filament length. The controlling parameters evaluated were the fibre length (l), the cement content (C), the porosity (η) and the porosity/cement ratio (η/C_iv). A number of unconfined compression and split tensile tests were carried out in the present work. The results show that fibre insertion in the cemented soil, for the whole range of cement content studied, and the increase of reinforcement length improve unconfined compressive and split tensile strengths. It was shown that the porosity/cement ratio, in which volumetric cementitious material content is adjusted by an exponent (0.28 for all the fibre-reinforced and non-reinforced cemented soil mixtures) to end in unique correlations for each mixture, is a good parameter in the evaluation of the unconfined compressive and split tensile strength of the fibre-reinforced and non-reinforced cemented soil studied. Analysis of variance (ANOVA) performed on the results of a factorial experiment considering the effect of adjusted cement content, fibre length and porosity showed that all of these factors are significant in affecting the measured changes in split tensile and unconfined compressive strength values. Finally, unique dosage relationships could be achieved linking the unconfined compressive strength (q_u) and the split tensile strength (q_t) of the sandy soil studied with porosity/cement ratio (η/C_iv) and fibre length (l).     

高温后沙漠砂混凝土抗压强度超声检测

考虑温度和沙漠砂替代率两个因素,对90个尺寸为100 mm×100 mm×100 mm沙漠砂混凝土立方体进行高温试验,通过对高温后试件进行抗压强度和超声检测试验,探究沙漠砂替代率和温度对抗压强度和超声波速的影响,建立高温后相对抗压强度劣化模型,得到沙漠砂混凝土高温后相对抗压强度与相对超声波速之间的关系,为沙漠砂混凝土高温后抗压强度的无损检测提供技术支撑。     

An investigation into the effects of lime on compressive and shear strength characteristics of fiber-reinforced clays

To meet the ever-increasing construction demands around the world during recent years,reinforcement and stabilization methods have been widely used by geotechnical engineers to improve the performances and behavior of fine-grained soils.Although lime stabilization increases the compressive strength of soils,it reduces the soil ductility at the same time.Recent research shows that random fiber inclusion modifies the brittleness of soils.In the current research,the effects of lime and polypropylene(PP) fiber additions on such characteristics as compressive and shear strengths,failure strain,secant modulus of elasticity(E_(50)) and shear strength parameters of mixtures were investigated.Kaolinite was treated with 1%,3% and 5% lime by dry weight of soil and reinforced with 0.1% monovalent PP fibers with the length of 6 mm.Samples were prepared at optimum conditions and cured at 35℃ for 1 d,7 d and28 d at 90% relative humidity and subsequently subjected to uniaxial and triaxial compression tests(UCT and TCT) under cell pressures of 25 kPa,50 kPa and 100 kPa.Results showed that inclusion of random PP fibers to clay-lime mixtures increases both compressive and shear strengths as well as the ductility.Lime content and curing period were found to be the most influential factors.Scanning electron microscopy(SEM) analysis showed that lime addition and the formation of cementitious compounds bind soil particles and increase soil/fiber interactions at interface,leading to enhanced shear strength.The more ductile the stabilized and reinforced composition,the less the cracks in roads and waste landfill covers.     

不同纤维掺量加筋土无侧限抗压强度分析

选用聚丙烯纤维为加筋材料,分别对红粘土、粉质粘土和砂土3种土体进行加筋,通过对不同纤维掺量的加筋土进行无侧限抗压强度试验,得到3种加筋土的无侧限抗压强度,并与各自素土的无侧限抗压强度进行比较,得到了一些有意义的结论。     

不同替代率下机制砂混凝土抗压强度的试验研究

抗压强度是混凝土的一项重要力学性能,为研究机制砂混凝土的抗压强度的变化规律,以选用的机制砂配制C50混凝土,在水泥用量和砂率保持不变的情况下,改变机制砂对天然砂的取代率(0、30%、50%、70%、100%)。通过比较分析试验数据得出以下结论:机制砂混凝土抗压强度大于天然砂;机制砂混凝土抗压强度随龄期的增长和替代率的提高而增大。混凝土在此基础上确定该机制砂的最佳替代率为50%。     

玄武岩纤维混凝土冲击压缩韧性

介绍了利用Φ100 mmSHPB装置获得玄武岩纤维混凝土冲击压缩在3种应变率范围下的应力-应变曲线的试验研究.并以应力-应变全程曲线所围面积作为韧性指标,对玄武岩纤维掺量分别为0、0.1%、0.2%和0.3%的混凝土在冲击荷载下增韧特性进行了对比分析.研究表明,在0～0.020应变范围内,4种掺量的玄武岩纤维混凝土中,BFRC0.2韧性最高,尤其在50/S～60/S应变率范围内,比素混凝土韧性指标提高了12.7%;应变较低时,一般素混凝土的韧性指标最高:与素混凝土相比,在应变率较低时,3组掺玄武岩纤维的混凝土韧性均有所提高,而在80/S～100/S应变率范围下,BFRC0.3韧性最低.     

钢纤维混凝土冲击压缩韧性

利用Φ100 mm SHPB装置分别对60 MPa 强度等级的素混凝土及钢纤维掺量分别为0%,0.2%,0.4%和0.6%的混凝土进行冲击压缩试验,控制在 10/s～20/s,30/s～40/s和75/s～90/s的应变率范围内.以峰值应变和残余强度法,作为韧度评价指标.峰值应变基本随钢纤维含量增加而增加,但随应变率的上升,钢纤维含量对峰值应变的影响减弱.对于C60系列,准静态下,最大增强27% (C60V4),83/s时,最大增强7%(C60V2);应变率86/s左右时,峰值应变基本与钢纤维含量无关.同样,残余强度对应的应变值明显随纤维含量增加而增加,反映出钢纤维的增韧效果.     

Coupling binder hydration,temperature and compressive strength development of underground cemented paste backfill at early ages

Cemented paste backfill (CPB) is an engineered mixture containing up to 60% solid tailings, and 3–7% binder (often) and water. CBP is used in backfilling underground mine voids. It receives great interest as one of the most commonly used ways in mine backfilling around the world. The usage of CPB greatly contributes to the disposal of mining tailings waste from the surface, increasing working place stability to extract more minerals safely. The key parameter for the design of CPB structure is its strength; namely, unconfined compressive strength (UCS). Knowing the time at which the CPB reaches its reasonable strength is very important for reducing the mining cycle and ensuring the safety of mine workers. As a cemented material, CPB strength is time and temperature dependent, and a function of the degree of hydration. The objective of this paper is to develop a numerical model for predicting the UCS of undrained CPB. Strength development is coupled with temperature and degree of hydration. For validation purposes, the predicted UCS will be compared with three groups of experimental results. The results show a good agreement between the predicted and measured values, and a new formula is suggested for including the effect of temperature into the UCS of CPB.     

The compressive strength experimental study of cemented soil under H2SO4 corrosive in earlier period

In order to simulate and study the erosion effect process such as the changes of corrosive depth and unconfined compression strength of cemented soil sample in earlier period from 0 day to 60 days, a series of tests including unconfined compressive tests, measuring the blocks＇ sizes, and taking photos, are conducted on the cemented soil blocks which were cured in different concentrations of H2SO4 solutions. The results of tests show that the corrosive depth is increasing and the unconfined compression strength is decreasing with the increase of H2SO4 solution concentration at the same erosion time, and the corrosive degree is increasing with the corrosive time. In the earlier state, the corrosive effect is serious, but the effect becomes slow in the later state in the same concentrated H2SO4 solution. After take statistics the date, a coefficient a is put forward to predict the reduction of the compressive strength of cemented soil in various concentration of H2SO4 solution, which could be used in practical design.