掺水泥粉土的改良风积沙三轴压缩特性

基于单掺5%水泥的经济性设计指标,开展了混掺水泥粉土的改良风积沙三轴压缩试验,分析了改良风积沙试样不同围压下的应力-应变及强度特性,揭示了不同掺比改良风积沙黏聚力和内摩擦角的变化规律,以及改良风积沙的破坏形式及剪切破坏机理。结果表明:改良风积沙的应力-应变关系曲线均为应变软化型曲线;弹性模量和破坏强度与围压正相关,弹性模量在粉土掺量增至15%时达到峰值;破坏强度与粉土掺量正相关;10%粉土掺量下改良风积沙黏聚力最大,内摩擦角则随粉土掺量增加而单调增长。水泥水化物包裹在沙粒表面,增加了沙粒表面粗糙度,并在沙粒之间的空隙形成网状结构,将沙粒联结起来,阻碍沙粒相对运动;掺入适量粉土可填充沙粒和水化物之间的空隙,但过量粉土会制约水化反应,同时碱性离子与水化物反应产生胶结能力差的硅酸钠和铝酸钠,导致改良风积沙整体性能下降。

水泥稳定粉土的施工实践

以河南省商丘至开封高速公路为例 ,主要阐述了水泥稳定粉土底基层的施工工艺、存在的问题。

水泥稳定粉土的施工工艺及质量控制

主要阐述了水泥稳定粉土的施工工艺、存在的问题。

水泥稳定粉土在公路工程中的施工及质量控制

本文通过作者多年的工作经验,结合某工程实例,主要对公路工程中的水泥稳定粉土底基层的施工技术进行分析,并着重针对工程中所存在的问题采取有效的措施,使其达到一定的规范要求。

水泥稳定粉土的施工实践

以某高速公路为例,主要阐述了水泥稳定粉土底基层的施工工艺、存在的问题、处理方法以及注意事项。

水泥基泡沫轻质粉土力学性能试验研究

为了探究粉砂土的不同掺量对水泥基泡沫轻质粉土力学性能的影响规律,针对工程常用的湿密度为700 kg/m3的泡沫轻质粉土,通过开展室内试验,对水泥基泡沫轻质粉土在不同粉砂土掺量(20%, 30%, 40%)条件下的无侧限抗压强度、饱水抗压强度、弯拉强度和静弹性模量进行了测试分析。试验结果表明:随着粉砂土掺量的提高,无侧限抗压强度、弯拉强度和静弹性模量先增大后降低,最优掺量为20%;相较于无侧限抗压强度,饱水抗压强度降低幅度较大,且随粉砂土掺量增加而降低。

水泥基粉土泡沫轻质土干湿循环特性试验研究

为了揭示水泥基粉土泡沫轻质土耐久性能,通过调整轻质土湿密度、粉土掺量等指标,研究了50次干湿循环过程中泡沫轻质土无侧限抗压强度的变化规律。结果表明,随着干湿循环次数的增多,泡沫轻质土的基本力学性能仅略有衰减,对于整体强度未产生显著影响,显示了良好的抗干湿循环特性。依据试验结果,建立了适用于不同配比的水泥基粉土泡沫轻质土无侧限抗压强度随干湿循环次数的数学预测公式。研究成果可为该材料的工程应用提供科学依据。

论水泥稳定粉土的施工方法

以高速公路为例,主要阐述了水泥稳定粉土底基层的施工工艺、存在的问题、处理方法以及注意事项。

水泥基粉煤灰粉土气泡混合轻质土性能研究

以粉煤灰和粉土部分替代水泥制备气泡混合轻质土,研究水固比、引气剂掺量、粉土掺量、养护龄期及养护条件对无侧限抗压强度影响和轻质土抗干湿循环性能。结果表明:降低水固比能够增大抗压强度;湿密度由1000 kg/m^(3)增大至1200 kg/m^(3),28天抗压强度提高了37%;随着粉土掺量增大,抗压强度降低;提高养护温度可提高早期抗压强度;制备的轻质土抗干湿循环性能较好。

水泥石灰综合稳定粉土压实标准探讨

临海高等级公路沿线土质普遍为粉土或粉土夹粉质黏土。当该土质作为底基层材料时,采用水泥石灰综合稳定较单一采用石灰稳定具有早期强度高、板体性好、表面不易松散等优势,但在足够的压实功作用下,压实度始终不能满足要求。通过大量的试验和现场检测,对压实标准做了研究和探讨,并与石灰稳定粉土进行综合比较,提出较为合理的解决压实度不足问题的方案。

Chloride diffusivity in flexural cracked Portland cement concrete and fly ash concrete beams

In order to examine the effect of load-induced transverse cracks on the chloride penetration in flexural concrete beams, two different concretes, Portland cement concrete(PCC) and fly ash concrete(FAC), were tested with various crack widths. Total 14 reinforced concrete(RC) beams, ten of which were self-anchored in a three-point bending mode, were immersed into a 5% NaCl solution with the condition of dry-wet cycles. Then, the free chloride ion contents were determined by rapid chloride testing(RCT) method. Based on the proposed analytical models of chloride penetration in sound and cracked concrete subjected to dry-wet cycles, the apparent chloride diffusion coefficient and chloride diffusivity of concrete were discussed. It can be found that the performance of chloride diffusivity in both concretes will be improved with the increase of crack width, and that the influence of convection action will also be augmented. Based on the two samples obtained in sound concrete after 15 and 30 cycles, the time-exponent, m, for chloride diffusion coefficient was determined to be 0.58, 0.42, 0.62 and 0.77 for PCC1, PCC2, FAC1 and FAC2 specimens, respectively. Finally, two influencing factors of fly ash content and crack width on chloride diffusivity were obtained by regression analysis of test data, and it can be seen that factors kf and kw can be expressed with quadratic polynomial functions of fly ash content, f, and crack width, w, respectively.

Talc-Based Concrete for Sealing Borehole Optimized by Using Particle Packing Theory

The paper describes assessment of the performance of cement-poor concretes on the basis of packing theory. The concretes are intended for sealing segments of deep boreholes and have a small amount of cement for minimizing the mutual chemical impact on the contacting clay seals. The composition is examined by application of packing theory with respect to the cement/aggregate ratio and the gradation of the aggregate material which is crushed quartzite for providing high internal friction after maturation, as well as to talc added for fluidity and to the small amount of cement. Low porosity and micro-structural stability must be guaranteed for very long periods of time. The study exemplifies how packing theory assist designers in selecting optimal proportions of the various components. Optimum particle packing implies minimizing the porosity and thereby reducing the amount of cement paste needed to fill the voids between the aggregate particles. The use of talc as inorganic super-plasticizer since ordinary organic additives for reaching high fluidity at casting are undesirable, and since talc reacts with cement and provides high strength in along-term perspective.

Effective Utilization of Coal Fly Ash in Building Material Production

This paper is aimed at verifying utilization possibilities of alkaline modified coal fly ash as cement replacement in the concrete. The influence of alkaline activated coal fly ash originating from Slovakian power plant in Novsky （Si/Al = 3,1） as a partial cement replacement in concrete on compressive strength of hardened composites after 28 and 90 days was investigated. Alkaline activation of coal fly ash was realized in an autoclave at 130 ℃ and pressure of 160 kPa during 5 hours and in a reactor under normal conditions （equal temperature during 36 hours） at solid/liquid ratio of 0.5. Coal fly ash/cement mixtures were prepared with 25 % cement replacement by starting and modified coal fly ash and given in forms. Compressive strengths of composites after 28 and 90 days of hardening were compared to referential composite without coal fly ash and evaluated according to the standard of STN EN 450 by the value of relative strength KR （compressive strength of coal fly ash/cement composite to compressive strength of comparative concrete）. The final compressive strengths of hardened composites based on alkaline activated coal fly ash reached values in the range of 6 up to 50 MPa. In the set of experimental composites based on alkaline activated coal fly ashes, the highest value of relative strength after 28- and 90- days of hardening reached composite with cement replacement by coal fly ash zeolitized in autoclave （105% of compressive strength of referential sample）, what is connected with formation of zeolitic phases on surface of coal fly ash particles. The achieved results confirm that alkaline activation of coal fly ash in an autoclave under observed conditions can be successfully used as a partial cement replacement in concrete of C20/25 and C25/30 in accordance with requirements of standards （STN EN 450 and STN EN 206）.

Properties prediction of fly ash blended concrete using hydration model

Fly ash is an industrial by-product from coal combustion and has been widely used as mineral admixture in normal and high strength concretes. Owing to the pozzolanic reaction between calcium hydroxide and fly ash, compared with Portland cement, the hydration of concrete containing fly ash is much more complex. In this paper, by considering the production of calcium hydroxide in cement hydration and its consumption in the pozzolanic reaction, a numerical model is proposed to simulate the hydration of concrete containing fly ash. Similar to the hydration reaction of cement, fly ash activity is divided into three processes: an initial dormant period, a phase-boundary reaction process and a diffusion process. The mutual interactions between the cement hydration and fly ash reaction are considered through the available calcium hydroxide amount and available capillary water amount in the system. The properties of hardening fly ash blended concrete, such as the reaction degree of fly ash, chemically bound water, calcium hydroxide, and compressive strength, are determined from the contributions of cement hydration and fly ash pozzolanic reaction. The evaluated results show good accordance with the experimental results.