ELECTRO-THERMAL EFFECTS AND DEFORMATION RESPONSE OF CARBON FIBER MAT CEMENT BEAMS

A carbon fiber mat is a sheet composed of intercrossing short carbon fibers,which has more stable and lower electrical resistivity compared with dispersed short carbon fiber mixed in cement.Thereby carbon fiber mat cement could exhibit obvious electro-thermal effect.When electrified,the temperature of composite structures made up of cement mortar and carbon fiber mat will rise rapidly.If the temperature field is not uniform,temperature difference will cause structures to deform,which can be used to adjust the deformation of structures.The temperature field and deformation response driven by the electro-thermal effects of a type of carbon fiber mat cement beams are studied.Firstly,the temperature and deformation responses are studied using theories of thermal conduction and elasticity.Secondly,experimental results are given to verify the theoretical solution.These two parts lay the foundation for temperature and deformation adjustment.

Size effect on cubic and prismatic compressive strength of cement paste

A series of compression tests were conducted on 150 groups of cement paste specimens with side lengths ranging from 40 mm to 200 mm. The specimens include cube specimens and prism specimens with height to width ratio of 2. The experiment results show that size effect exists in the cubic compressive strength and prismatic compressive strength of the cement paste, and larger specimens resist less in terms of strength than smaller ones. The cubic compressive strength and the prismatic compressive strength of the specimens with side length of 200 mm are respectively about 91% and 89% of the compressive strength of the specimens with the side length of 40 mm. Water to binder ratio has a significant influence on the size effect of the compressive strengths of the cement paste. With a decrease in the water to binder ratio, the size effect is significantly enhanced. When the water to binder ratio is 0.2, the size effects of the cubic compressive strength and the prismatic compressive strength of the cement paste are 1.6 and 1.4 times stronger than those of a water to binder ratio of 0.6. Furthermore, a series of formulas are proposed to calculate the size effect of the cubic compressive strength and the prismatic compressive strength of cement paste, and the results of the size effect predicted by the formulas are in good agreement with the experiment results.

Analysis on Impacts and Co-Abatement Effects of Implementing the Low Carbon Cement Standard

Based on the MAP-CGE model,this paper simulated the impacts on the output,energy consumption and pollutant emissions of different cement production processes when implementing a low carbon cement standard in China.It also calculated the impacts on the marginal abatement cost and equilibrium price of the cement industry,and analyzed the co-abatement effects of different pollutants.The results showed that implementing the low carbon cement standard will be beneficial in promoting an upgrading of cement production processes,and strengthening the energy conservation and emission reduction in the cement industry.If there is no change in the existing technology,the cement industry will reduce SO2emissions by 1.17 kg and NOxemissions by 4.44 kg per ton of CO2emission reduction.Implementing low carbon cement standard can also promote NOxabatement in the cement industry.However,the cement industry will bear the abatement costs,and their equilibrium price will increase slightly.

THE EFFECT OF POLYMER IN STEEL FIBER REINFORCED CEMENT COMPOSITES

Three kinds of polymers, polymethyl acrylate emulsion (POLYVINYLformal solution (PV- FO), styrene acrylate copolymer emulsion (SA)are chosen To study the effect of polymer in steel fiber rein forcedce- Ment composites (SFRCC). The experimental results show That thebonding properties in SFRCC are remarkably im- Proved after theaddition of three kinds of polymer.

Effects of Specimen Shape and Size on Water Loss and Drying Shrinkage of Cement-based Materials

The effects of specimen size and shape on development of water loss and shrinkage of mortar and concrete respectively were investigated. The experimental results showed that the effects of specimen size and shape on water loss ratio were consistent with those on drying shrinkage strain. It is also indicated that drying shrinkage strain has obvious linear correlation with water loss ratios independent of specimen size and shape. The effects of specimen size and shape on the water loss ratio were embodied in established model of averaged relative humidity improved by considering effects of sequential hydration and calculated by finite difference method. Furthermore, the effects of specimen size and shape on drying shrinkage strain of concrete were experimentally deduced and applied to modify criterion EB-FIP1990. The comparison between experimental and calculated results shows that the modified EB-FIP1990 can be adopted to predict drying shrinkage strain of concrete with reasonable accuracy.

STRENGTH EFFECT OF F MINERAL ADMIXTURE ON CEMENT CONCRETE

F mineral admixture (FMA) is made of the fin- ely divided powder of natural zeolite with a bit of other agent. When FMA is used to displace about 10% (by weight) of the ordinary portland cement (OPC) (strength grade 575#) in concrete and mixed with a suitable amount of super plasticizer (w/c =0.31-0.35), then a high-strength concrete with compressive strength about 80 MPa and slump about 180 MM can be obtained. The strength of this concrete is about 10-15% higher than that of the corresponding concrete mixing with pure OPC, and its bleeding decreases greatly. It makes no segre- gation and separation, and thus it satisfies the requirement of pumping concrete in construction.

Mechano-electric Effect of Hardened Cement Paste During Quasi-static Loading

Mechano-electric effect of cement paste was investigated in this paper. As compressive stress was applied on the specimen, an electrical current was observed. The intensity of the electrical current increased with stress increasing, and decreased with stress decreasing. Different measurement methods were also discussed in this paper. This phenomenon was related to the electrokinetic phenomenon of solid/liquid interface in cement paste. The study on mechano-electric effect of hardened cement paste provides a new method for making smart concrete structures.

Effect on Hydration and Hardening of Tricalcium Phosphate Bone Cement

The bioactive α-Ca3（ PO4 ）2 bone cement was studied by XRD , SEM and isothermal calorimetric measurements. The results showed that a mixed pattern of TCP and hydroxylapatite were obtained after hydration and hardening. The mechanism of hydration and hardening of the α-Ca3 （ PO4）2 was dissolution-precipitation, （ NH4 ） 112 PO4 was the best set accelerator to the α-Ca3 （ PO4）2 cement, and the HAP powers and the （ NH4）H2 PO4 concentration had a great effect on the hydration rate of a-Ca3（ PO4）2.

Effect of the Cavity-Cavity Interaction on the Stress Amplitude in Orthopedic Cement

The presence of porosities in bone cement (polymethylmethacrylate) in total hip prosthesis (THP) cemented is necessary for the diffusion of antibiotics, but it is a critical characteristic of weakening by the effect of stress concentration and the interconnecting pores. The aim of this study was to analyse by the finite element method (FEM), the size influence of micro-cavities in cement assuming the junction cup-bone, and the effect of cavity-cavity interaction on the stress level and distribution in cement according to the human stance defined by the implant position axis compared to that of the cup.

Effect of soaking time of dithionite-citrate-bicarbonate solution on strength and deformation characteristics of lateritic soil

This study aimed to reveal the influence of different free-iron-oxides contents on the strength and deformation characteristics of in situ lateritic soil.A test method that combined the selective chemical dissolution method and in situ Ménard pressuremeter test(PMT)was proposed.The soaking time in dithioniteecitrateebicarbonate(DCB)solution was used as a variable to control the free-iron-oxides content in lateritic soil.Then,the in situ lateritic soil boreholes with different soaking time were tested by PMT.The results showed that the in situ horizontal pressure p0,critical edge pressure pf,ultimate pressure prediction pl,pressuremeter modulus Em,shear modulus Gm,and foundation-bearing capacity f0k of lateritic soil decreased rapidly after immersing in DCB solution within 1e4 d.With increasing soaking time,the decrease rate reduced gradually.Moreover,the relationship curve between free-iron-oxides content and soaking time declined rapidly and then stabilized,and the free-iron-oxides content at the inflection point was 30.11 g/kg.When the free-iron-oxides content changed to the inflection point,the free-iron-oxides that played a cementing role was largely removed,indicating that the effective cementing iron-content of Miaoling lateritic soil was about 52.9%.This study demonstrated that the proposed test method can determine the influence of free-iron-oxides content on the strength and deformation characteristics of lateritic soil.

Characterization of Thermo-Physical Properties of Cement-Based Blocks of Varied Sand Types Using Cost-Effective Enhancement Approach

The dominant property of building envelope fabric which contributes significantly to minimize electricity utilization in building is the thermo-physical properties. There is inadequate literature on representative practical data of thermo-physical properties of the dominant building envelope components in Ghana. This study aims to use cost-effective approach to characterize the thermo-physical properties of only cement-based mortar and concrete blocks used in Ghana for building components specifically wall design. Mixed methods research design was employed to achieving the aim. A questionnaire survey was used among sampled building fabric components manufacturers to pick representative data on thermos-physical properties of their mortar and concrete blocks. Also, an experimental procedure employing a transient technique with a TCi Thermal Analyser was used to determine the thermo-physical properties of selected mortar and concrete blocks from Ghana in addition to designed parametric mortar and concrete blocks with varied ratios obtained from the survey were undertaken at University of Nottingham. From the study, a trend of decreasing thermal conductivity and thermal effusivity with corresponding decreasing sand content was observed with all the different sand types. The thermal conductivities of both mortar and concrete parametric blocks meet the range of expected standard values outlined in Chattered Institute of Building Services Engineers (CIBSE) Guide A. The major limitation of the work is the dimension of the sample size;which is not inconsistent with standard block size due to the experimental setup used. It is expected that, the characterization of the predominant cement-based building fabrics components will contribute to improved building performance analysis with significant savings in electricity utilization for space cooling.

工业废弃木质素固化土特性及其在岩土工程中的应用进展

为明确工业废弃木质素在岩土工程中的应用现状和存在问题,探寻用于突破现有木质素改良土体技术的科学方法和工程措施,笔者在已有研究基础上,介绍了木质素在岩土工程中的应用状况,探讨了木质素与土体间的相互作用机制,指出了需要解决的关键问题和下一步研究的方向。结果表明:木质素对砂性土和黏性土均具有提高力学性能、抵抗水分侵入的效果,土体的韧性特征得到明显提高;木质素产生的胶结作用是土体微观结构和宏观工程性质改善的根本原因,阐明胶结物质的生成机制是揭示其改良土体机制的关键;木质素固化土在恶劣环境中的耐久性能需进一步提升,相应的施工工艺和工程防护措施仍不完备;对木质素进行化学改性,增强其胶结与耐久性能,系统研究土颗粒胶结与改良土的应力应变特征以及扩宽木质素的土体处置对象均是值得继续深入研究的科学问题。

结构性土中圆柱孔扩张不排水解答及结构退化影响分析

圆孔扩张理论为桩基挤土位移预测和旁压试验结果分析等提供了理论依据,而现有解答中缺乏对土体结构影响的系统分析.基于考虑胶结作用的模型Cemented-CASM,推导了反映土体应力-应变关系的弹塑性刚度矩阵,在此基础上联立硬化法则和大应变理论,得到了不排水条件下结构性土中圆柱孔扩张问题的弹塑性解答.在不考虑土体结构性时,将退化解答与已有修正剑桥模型解答进行比较;在考虑结构性影响时,与旁压试验数值模拟结果比较,验证了解答的可靠性.通过参数分析说明了结构性及其退化对圆柱孔扩张过程的影响,结果表明:与重塑土相比,结构性土中扩孔引起的有效应力和孔隙水压力更大,而孔周塑性范围更小;随着结构的破坏,孔周土体表现出应变软化特征,径向应力随到孔壁距离的减小呈先增后减的变化趋势;土体结构完全破坏时,其有效应力与重塑土中趋于一致;土体结构性越强,相同扩孔压力或孔径变化下结构退化越快,软化特征越明显.

骨水泥强化椎弓根螺钉固定对腰椎椎管狭窄伴骨质疏松患者椎间融合率的影响及其远期效果分析

目的探讨骨水泥强化椎弓根螺钉固定对腰椎椎管狭窄伴骨质疏松患者椎间融合率的影响及其远期效果。方法选取本院2019年7—12月收治的52例腰椎椎管狭窄合并骨质疏松患者,随机分为实验组和对照组,每组26例,对两组患者施行椎板减压、椎间盘摘除、椎间植骨融合、椎弓根钉内固定术治疗。实验组采用骨水泥强化椎弓根钉固定,对照组采用普通椎弓根钉固定。记录患者疗效相关评分,术后半年进行腰椎X光检查了解椎间融合情况。结果两组患者在术前及术后2周的VAS评分、JOA评分及ODI评分差异并无统计学意义(P>0.05);而术后3个月时起至术后2年的VAS评分、JOA评分及ODI评分对比具有明显差异,具有统计学意义(P<0.05);术后半年通过Bridwell标准判断两组患者的椎间融合率时也发现两者具有显著差异,实验组患者椎间融合率明显高于对照组,且差异有统计学意义(P<0.05)。结论骨水泥强化椎弓根钉固定技术能有效提高椎体间植骨融合率,患者术后两年疗效令人满意,尽管目前对该技术的安全性仍有部分争议,但总的来说是利大于弊的,值得在临床上进一步推广。

川西地区气井环空带压条件下水泥环裂缝封堵规律研究

川西地区弃置井环空带压普遍存在,有效封堵水泥环裂缝对于防止天然气泄漏和地下水污染具有重要意义。尤其是在环空带压的条件下,裂缝的封堵难度增加,对封堵技术和材料的选择提出了更高的要求。文章利用高温高压岩心多参数测量仪开展了裂缝内封堵剂流动性能模拟测试实验,采用数值模拟方法研究了不同压差下柔性堵剂在裂缝内的流动规律,评价了常规油井水泥和柔性堵剂在弃置井环空带压条件下的流动性能。研究结果表明当裂缝开度在207μm以下时,增大驱替压力,无法有效增加柔性堵剂的流动性;当裂缝开度在383μm以上时,增大驱替压力,可显著提升柔性堵剂的流动性,进而提高封堵效率;当裂缝开度在446μm以下时,增大驱替压力值,无法有效增加常规油井水泥的流动性;当裂缝开度较小时,柔性堵剂在裂缝内的流动属于层流流动,流动层次分明、平滑且有序;采用波动压力的注入方式可提高堵剂的封堵效率。文章为环空带压弃置井柔性堵剂的流动性能测试及评价提供了实验和数据支撑,同时为弃置井封堵作业中封堵剂的合理选择提供了理论依据。

静态破碎剂性能分析及致裂效果实验研究

为解决现有煤矿井工开采过程中预裂爆破安全性低、适用性差以及水压致裂条件苛刻,破岩效果弱的问题,提出静态致裂的方法,通过研究不同影响条件下静态破碎剂的反应状态和致裂效果,对不同拌合水温、水灰比条件下的静态破碎剂反应温度、反应时间、反应体积变化、岩样致裂效果、应力变化进行了研究。结果表明:水灰比一定,静态破碎剂完全反应时间随拌合水温升高而降低,但最终反应完全后温度不变;相同拌合水温条件下,水灰比越小,静态破碎剂反应时间越短,反应速率越快;水灰比越小,混凝土试件开裂时间越短,水灰比越大,开裂时间越长,开裂效果与裂缝位置有关,块体应变呈现先增后减的趋势。

定向钢纤维增强水泥基复合材料准脆性断裂分析

基于边界效应模型基本理论,建立了钢纤维长度与特征裂缝长度之间的关系,计算了定向钢纤维增强水泥基复合材料(ASFRC)的等效断裂韧度和拉伸强度,进而得到了ASFRC材料的断裂破坏曲线.结果表明,当离散系数分别取0.4~0.7和0.2~0.4时,可得到较为合理的等效断裂韧度和拉伸强度值.对比分析ASFRC和随机乱向钢纤维增强水泥基复合材料(SFRC)的断裂破坏曲线可以发现,满足线弹性断裂力学的最小试件尺寸随着离散系数的增大而增大;ASFRC和SFRC的拉伸强度和考虑初始裂缝影响的名义应力随着离散系数的增大而减小.此外,改进的简化解析公式不仅可确定材料的等效断裂韧度和拉伸强度,还可预测试件的破坏.

3D打印水泥基材料高温后劈裂拉伸尺寸效应试验研究

为探究3D打印水泥基材料高温后劈裂拉伸尺寸效应,共设置5种温度和3种尺寸,应用液压伺服机对3D打印水泥基材料展开劈裂拉伸力学性能试验研究,分析高温和尺寸效应对3D打印水泥基材料劈裂拉伸力学性能的影响规律。主要得到以下结论:随着温度升高,试件抗拉强度逐步降低,不同尺寸试件的抗拉强度受高温影响降低幅度基本相同,最大降低幅度为87.97%。随着尺寸增加,试件抗拉强度逐步降低,温度的提高导致试件抗拉强度受尺寸效应影响变化幅度逐步增大。受尺寸效应影响,不同试件高温后的抗拉强度变化区间为18.488%~26.165%。同时,基于尺寸效应律提出3D打印水泥基材料高温下抗拉强度计算模型,并应用微观测试技术揭示其力学性能演化机理。

胶结充填体拱效应作用下的水平矿柱回采安全厚度研究

通过建立三维胶结充填体拱应力模型,得到胶结充填体竖向荷载计算公式,并根据四边固支顶板模型和岩体极限抗拉强度准则,得到了水平矿柱回采安全厚度确定方法。在某铅锌矿612采场水平矿柱回采的运用实践表明,解析模型计算的胶结充填体竖向应力与数值模拟结果基本吻合,数值模拟中顶板未出现塑性区,验证了计算确定的保留顶板厚度满足安全生产需求;回采过程监测结果表明,监测点附近的最大累计位移低于极限位移,保留顶板趋于稳定,确定的水平矿柱回采安全厚度具有足够的可靠性。

基于深度强化学习的C+L波段弹性光网络频谱分配算法

针对C+L波段弹性光网络中受激喇曼散射(SRS)效应导致物理层损伤加剧的问题,提出一种基于深度强化学习(DRL)自适应调制格式的频谱分配算法,在路由阶段,采用K最短路由算法为业务请求预计算K条最短备选路径;在波段、调制格式与频谱分配阶段,采用DRL进行智能化决策,并结合了2种奖励函数,以降低网络阻塞率并提高频谱使用效率。仿真结果表明,该算法能够有效降低阻塞率并提高频谱利用率。