Features of compressive failure of brittle materials

Experimental investigations of failure of continuous brittle materials are described for various loading modes: uniaxial compression, bending of longitudinal compressed beams, and multiaxial compression. For all these loading modes, compressive cracks developed under certain conditions. The conditions of their formation are established. The formation of compressive cracks coincided with the limiting state of the system (the peak of failure load). The bearing capacity of the system depended on the material-crushing resistance. Shear failure of continuous brittle materials also took place, but only at post-peak state after a material failure by tensile and compressive cracks.     

Optimum usage of a natural pozzolan for the maximum compressive strength of concrete

Pozzolans provide an economic production possibility in the concrete industry and improve the properties of concrete, such as durability. Effects of a pozzolan on the properties of concrete vary with the pozzolan type and volume.In this study, effect of a natural pozzolan on the properties of concrete was investigated. Fifteen concrete mixtures were produced in three series with control mixes having 300, 350 and 400 kg cement content. These control mixes were modified to have a combination of 250, 300 and 350 kg cement content and 40, 50, 75 and 100 kg pozzolan addition for 1 m³ concrete. The efficiency of the pozzolan was obtained by using Bolomey and Feret strength equations on 28-day-old concretes. Maximum pozzolan amount with the optimum efficiency was determined. This study shows that the efficiencies obtained from each strength equations are similar and these values decrease with the increase of pozzolan/cement ratio.     

燕南断裂带封堵性分析

辽河坳陷东部凹陷葵花岛断裂背斜构造带由燕南断裂带控制发育，是渤海海域的重要油气勘探区。燕南断裂带是郯庐断裂的组成部分，其断裂绝大多数是正断层。钻于该断裂带西侧的７口井证实，已见油气的４口井油气层均靠断面封闭。利用测井资料分析断裂结构面力学性质，认为断面很致密，发育断层泥（ＫＨ４井２４０２ｍ深度断面能够封闭的最大油柱高度为６７．４８ｍ）；根据横切断裂的地震剖面（道积分剖面），认为广泛发育断层泥；根据流体性质、压力系统和断面图分析，各断块互不连通，断裂两盘砂岩有相接处，靠断层泥封闭。燕南断裂带主要活动时期为早第三纪沙河街组和东营组沉积期，该阶段断裂间歇性活动，断面开启与封闭交替；馆陶组沉积期以来，断裂活动微弱，根据葵花岛构造带异常地层压力形成时期和油气显示层位，认为断裂带在东营组沉积期末形成封闭。图５参１０（王孝陵摘）     

Management of arsenic-laden water plant sludge by stabilization

When arsenic is co-precipitated with iron hydroxide in an arsenic-removal water plant, a large quantity of sludge is generated which contains a good amount (an average of 6.1 kg As/m³ of sludge) of arsenic. The present paper attempts to find some suitable solutions to disposal of this arsenic-bearing sludge. As a safe means of disposal, stabilization processes such as briquette production, cement mortar and concrete making have been attempted in the present investigation. It has been found that in the preparation of briquette, cement–sand mortar and concrete, mixing up to 10, 18 and 40% of arsenic-bearing sludge by volume, respectively with the other common ingredients did not produce a TCLP leachate beyond its permissible direct inland water discharge standards of 0.2 g/m³ as stipulated by the Ministry of Environment & Forest, Government of India. Also, it was noted that 25% (by volume) of cement could be replaced by fly ash to stabilize arsenic-laden sludge to the tune of 11% by volume of cement–sand (1 : 3) mortar.     

Setting time: An important criterion to determine the length of the delay period before steam curing of concrete

Some precast concrete plants expose freshly made concrete elements to steam curing immediately after casting. This is detrimental to properties of the product; therefore, some delay prior to the steam curing process is beneficial. This paper contains the results of an investigation on the effects of various delay intervals selected based on initial setting time of concrete. Four different delay periods and two different steam curing periods at 80 °C (5 and 10 h) were used with two concrete types, namely C25 and C40. Compressive strength tests were performed at 1, 3, 7, 28, and 90 days. Setting time of the concrete was found to be an important criterion to determine the length of the delay periods.     

YW—1无机胶粘接机理的探讨

本文从化学、物理、机械三方面深入地探讨了YW-1无机胶套接粘接形成高强度的原因。     

Prevention of back injuries in healthcare workers

A laboratory study was conducted to evaluate five different manual techniques (two-person lifting; rocking and pulling the patient using a gait belt with two persons; walking belt with handles with one and two persons; and a patient handling sling with cutouts with one person) for transferring patients from wheelchair to toilet and toilet to wheelchair. In addition, three different mechanical hoists (H, T and A) were studied for transferring patients from toilet to wheelchair. Six female nursing students with prior patient transfer experience served both as nurses and passive patients.

The mean trunk flexion moments, erector spinae muscle forces and compressive forces for the four manual pulling methods ranged from 93 to 133 Nm, 1861 to 2653 N and 1974 to 2745 N, respectively, as compared to about 200 Nm, 4100 N and 4800 N for two-person manual lifting. Manual lifting was perceived to be the most stressful by the nurses and the least comfortable and secure by the patients. Hoist A was perceived to be the least stressful and the most comfortable and secure. Hoists H and T were perceived to be more stressful, less comfortable and less secure than the walking belt.

An intervention study was conducted in two units of a nursing home (140 beds and 57 NAs) to determine the effectiveness of ergonomic changes. Nursing assistants (NAs) in the two units of the nursing home were trained in the use of selected devices and shower rooms and toilets were modified. The mean acceptability rates for walking belt and hoist A were 81% and 87%, respectively. The reported incidence and severity rates for back injuries over 13 months decreased from 83 to 43 and from 634 to 0, respectively, after the intervention. Nursing assistants perceived their job as “very light” after the intervention as compared to between “somewhat hard” and “hard” before intervention.     

Relationship between ultrasonic velocity and compressive strength for high-volume mineral-admixtured concrete

Ultrasound is used to evaluate the compressive strength of concrete with mineral admixtures. In addition, the relationship between ultrasound velocity and compressive strength of concrete are evaluated. High-volume fly ash (FA), blast furnace slag (BFS) and FA+BFS are used as the mineral admixtures in replacement of Portland cement (PC).

Compressive strength and ultrasonic pulse velocity (UPV) were determined at the 3-, 7-, 28- and 120-day curing period. Both compressive strength and UPV were very low for all the levels of mineral admixtures at an early age of curing, especially for samples containing FA. However, with the increase of curing period, both compressive strength and UPV of all the samples increased. The relationship between UPV and compressive strength was exponential for FA, BFS and FA+BFS. However, constants were different for each mineral admixture and each level replacement of PC.     

Influence of a thermal cycle at early age on the hydration of calcium sulphoaluminate cements with variable gypsum contents

Hydration of a belite calcium sulphoaluminate cement was investigated over one year as a function of its initial gypsum content (variable from 0 to 35%). Particular attention was paid to the influence of the thermal history of the material at early age on its subsequent evolution. Pastes and mortars (w/c 0.55) were either cured at 20 °C or submitted for one week to a thermal treatment simulating the temperature rise (up to 85 °C) and fall occurring in drums of cemented radwastes. The thermal cycle accelerated the early stages of hydration and mainly decreased the proportion of AFt versus AFm hydrates, especially at low initial gypsum contents (≤ 20% by weight of cement). It also strongly reduced the compressive strength of gypsum-free specimens (by 35% after one year), and doubled their expansion under water. These results were explained by mineralogical evolutions towards a more stable phase assemblage which included retarded ettringite formation.     

Compressive behaviour of nanoclay modified aerospace grade epoxy polymer

Abstract

The effect of nanoclay on the compressive response of an aerospace grade epoxy polymer was studied. The resin was modified with montmorillonite clay type nanomer I.30, and compressive tests were performed on the optimised specimen geometry. A series of nanocomposite with 1–5 wt-% nanoclay content was fabricated using mechanical stirring and three-roll mill methods. The degree of dispersion of the clay nanoplatelets was examined using TEM. Static uniaxial compression tests were conducted. The compressive stress–strain curves showed that the presence of nanoclay improved the compressive strength and stiffness, promoted higher plastic hardening behaviour after yielding and enhanced the fracture toughness (area under σ–? curve) of the epoxy polymer. The fracture surfaces of the broken specimens were observed using SEM with the aim to identify critical failure mechanisms that contributed to the polymer toughening. Rule of mixtures, Halpin–Tsai and modified Halpin–Tsai models were employed to estimate the compressive modulus of the clay–epoxy nanocomposite system.