Effect of temperature on the residual compressive strength of laterized concrete

Tests are reported on 100 mm laterized concrete cubes, containing ordinary portland cement, crushed granite, sharp sand and fine laterite in varying proportions. The percentage of sand by weight of total fine aggregate was varied in steps of 25% up to a maximum of 100% corresponding to normal concrete. The mix proportion was . The test specimens were exposed to varying temperatures ranging from 30°C (i.e. room temperature) to 800°C and allowed to cool for 24 hours before crushing. The results showed that unlike normal concrete the residual compressive strength of laterized concrete increaed, by up to 50% of the nominal strength, with increasing temperature up to 200°C before falling to about 20% of the nominal strength at 800°C. The gain in strength depended on the sand content. The results further showed that within the limits of water/cement ratios normally used in concrete works (i.e. 0.55 to 0.65), the residual strength of laterized concrete was independent of the water/cement ratio. Also, the density of laterized concrete was not significantly affected by changes in temperature but that the tangent modulus of elasticity was reduced from 18 kN/mm² at 30°C to 0.12 kN/mm² at 600°C.     

People''s clothing behaviour according to external weather and indoor environment

In prehistoric times man wore furs of animals to protect himself from the cold. Successively over the centuries clothing has become also a tool to distinguish ourselves in society. Clothing has in addition an important impact on people's perception of the indoor environment.

Clothing behaviour has been analysed by investigating the external and indoor parameters that motivate people's choice of clothing. Based on two existing databases, two types of buildings have been investigated: air-conditioned and naturally ventilated (NV) buildings. The impact of outdoor temperature on people's clothing selection has been considered. The outdoor temperature at 6 a.m. seems to affect people's choice of clothes the most. Gender does not significantly affect the selection of clothing insulation.

Latitude has also been investigated and a good correlation has been found between clothing insulation and external temperature in the ranges 20°–40° and −20° to −40° for NV buildings.

Indoor air temperature does not seem to influence the clothing choice early in the morning but it does seem to influence the change of clothing during the day, if this is authorized, in workplaces in NV buildings. Such action can be termed “clothing adjustment” during the day.

Some computer simulations on a test reference year have been carried out for a typical air-conditioned office to analyse a person's comfort when wearing different clothes. It is possible to see that in air-conditioned buildings a variation of 0.1 clo is sufficient to change totally the comfort evaluation. It is evident that further studies are needed in this field.     

Field study on occupants’ thermal comfort and residential thermal environment in a hot-humid climate of China

This paper discusses thermal comfort inside residences of three cities in the hot-humid climate of central southern China. Only a few thermal comfort studies have been performed in hot-humid climates and none in Central Southern China. Field sampling took place in the summers of 2003 and 2004 by obtaining 110 responses to a survey questionnaire and measuring environmental comfort variables in three rooms in each of 26 residences. The objectives are to measure and characterize occupant thermal perceptions in residences, compare observed and predicted percent of dissatisfied and discern differences between this study and similar studies performed in different climate zones. Average clothing insulation for seated subjects was 0.54 clo with 0.15 clo of chairs. Only 48.2% of the measured variables are within the ASHRAE Standard 55-1992 summer comfort zone, but approximately 87.3% of the occupants perceived their thermal conditions acceptable, for subjects adapt to prevailing conditions. The operative temperature denoting the thermal environment accepted by 90% of occupants is 22.0–25.9°. In the ASHRAE seven-point sensation scale, thermal neutral temperature occurs at 28.6°. Preferred temperature, mean temperature requested by respondents, is 22.8°. Results of this study can be used to design low energy consumption systems for occupant thermal comfort in central southern China.     

Thermal comfort study of young Chinese people in Hong Kong

The purpose of this study is to investigate the thermal comfort of college-age Chinese subjects and obtain the optimum thermal conditions for buildings. 134 college-age Chinese subjects wearing 0.6 clo standard clothing were exposed under sedentary activity for 3 h to several different thermal conditions. The neutral temperature of young Hong Kong Chinese was found to be 24.9°C. This is not significantly different from previous studies with Danish and American subjects. Using the probit technique for analysing subjective responses of thermal sensation the neutral zone was found to be between 22.2 and 25.2°C.     

Observations of upper-extremity skin temperature and corresponding overall-body thermal sensations and comfort

This paper explores how upper extremity skin temperatures correlate with overall-body thermal sensation. Skin temperature measurements of the finger, hand, and forearm might be useful in monitoring and predicting people's thermal state. Subjective perceptions of overall thermal sensation and comfort were collected by repeated surveys, for subjects in a range of test chamber temperatures. A positive temperature gradient (finger warmer than the forearm) of as much as 2 K was seen when subjects felt warm and hot, while a negative temperature gradient (finger colder than the forearm) as much as 8.5 K was seen for cool and cold subjects. A useful warm/cold boundary of 30 °C was found in finger temperature, for both steady state and transient conditions. When finger temperature was above 30 °C, or finger-forearm skin temperature gradient above 0 K, there was no cool discomfort. When finger temperature was below 30 °C, or the finger-forearm skin temperature gradient less than 0 K, cool discomfort was a possibility. Finger temperature and finger-forearm temperature gradient are very similar in their correlation to overall sensation. We also examine how overall sensation is affected by actively manipulating the hand's temperature.     

Assessment of thermal environment using a thermal manikin in a field environment chamber served by displacement ventilation system

This paper presents a thermal comfort study using a thermal manikin in a field environment chamber served by the Displacement Ventilation (DV) system. The manikin has a female body with 26 individually heated and controlled body segments. The manikin together with subjects was exposed to 3 levels of vertical air temperature gradients, nominally 1, 3 & 5 K/m, between 0.1 and 1.1 m heights at 3 room air temperatures of 20, 23 and 26 °C at 0.6 m height. Relative humidity at 0.6 m height and air velocity near the manikin and the subjects were maintained at 50% and less than 0.2 m/s, respectively. The aims of this study are to assess thermally non-uniform environment served by DV system using the manikin and correlate the subjective responses with measurements from the manikin. The main findings indicate that room air temperature had greater influence on overall and local thermal sensations and comfort than temperature gradient. Local thermal discomfort decreased with increase of room air temperature at overall thermally neutral state. The local discomfort was affected by overall thermal sensation and was lower at overall thermally neutral state than at overall cold and cool sensations.     

The maturity method: Modifications to improve estimation of concrete strength at later ages

Two modifications have been proposed for the Nurse–Saul maturity function to get better estimates of compressive strength of concrete cured at different temperatures. The modifications account for the effect of w/c ratio on the temperature dependence of strength development and the effect of curing temperature on the long-term strength. The effect of the proposed modifications on the estimation of concrete strength using the Nurse–Saul maturity function have been compared with the estimation using unmodified Nurse–Saul equation with two different datum temperatures (i.e., T₀ = −10 °C and T₀ = 0 °C). The results show that applying the proposed modifications improves the accuracy of estimated concrete strength at different curing temperatures, especially at later ages.     

Useful solar gains through a glazed south-facing wall in the U.K. climate

A glass skin attached to a southfacing wall may serve to direct a sizeable fraction of the solar gain absorbed at the outer surface of the wall to the wall interior. The heat flow may help to make good ventilation heat losses, and conduction losses to other parts of the building. A wall of high thermal resistance tends to restrict this flow, but it also restricts the outward flow of heat. For given conditions there may be an optimum thickness. Tables are presented giving the heat needs for an unglazed wall, and for a wall with one or two glass skins attached to it. The variation in heat need with choice of month, ventilation loss and comfort temperature is shown as a function of the wall resistance. The results are based on weather data for the north Wirral, U.K. 53.4° N.     

A critique of the environmental temperature model

For many years, the index temperature to describe the warmth of a room was termed ‘air temperature’, t_ai. This was not logical since the index was taken to drive a longwave radiant flux to a room surface, in addition to driving the convective flux that is properly associated with air temperature. Environmental temperature, t_ei was introduced in the 1960s; it was composed of air and surface temperature components and was intended to replace air temperature as the room index. Certain compound conductances were associated with t_ei and the package of ideas was incorporated into the 1970 IHVE Guide to carry through calculations which involve heat transfer with the surfaces of a room.

The procedure—the environmental temperature model—has not proved easy to understand. The model is based on three erroneous ideas: it reduced the 21 conductance network that represents radiant exchange in a six surface enclosure to just a single conductance, and so failed to distinguish between emissivity and geometrical aspects of radiant exchange; the argument appeared to suggest—wrongly—that the temperature t_ei so arrived at was a meaningful enclosure parameter; it assumed—also wrongly—that heat could be input at t_ei. This t_ei is a nonsensical quantity and the model leads to some absurd conclusions. The value of t_ei as it is evaluated is a different quantity from t_ei as it is defined and is numerically larger when heat is input radiantly to the enclosure. The operational value of t_ei has a valid theoretical basis for an elementary enclosure but in general it oversimplifies enclosure heat exchange and may lead to somewhat crude numerical estimates. The environmental temperature model comprises conductances, heatflows and the temperature t_ei itself which are based on a mixture of convective and radiant processes. The model is unable to express radiant temperature in explicit circuit form. ‘Mean radiant temperature’ (mrt) should denote either the space-averaged observable temperature, or the star temperature of the star pattern used to express radiant exchange; both are global parameters and both are needed. In fact the CIBSE Guide sees mrt as a local parameter, which is inappropriate, and actually identifies it with mean surface temperature, which is grossly in error. Finally the expression for comfort or dry resultant temperature is conceptually inappropriate.     

Room size and adequacy of space in small homes

Postal and interview surveys of recently constructed starter homes were conducted in 15 areas of England and Scotland. The surveys recorded subjective ratings of room size and adequacy of space. Overall, 63% of respondents said they did not have enough space and 67% said they found it inconvenient to have visitors or overnight guests. Whether a starter home is perceived as having enough space seems to be related more to the number of occupants than the physical size of the home, and also varies with household income, the respondent's working status, geographical region and window area.     

Measurements of room air distribution in a ventilated office environment

Results of measurements of the room air flow properties in an office space environment (4.74 m × 4.87 m × 2.87 m) with and without partitions (acoustical screens) are presented. The measurements included air flow pattern, air speed, and turbulence intensity. The profiles of the mean speed and the turbulence kinetic energy at the supply air opening are also presented. The data show the effect of using acoustical screens (with various heights and a gap between the floor and the bottom of the screen) on the air flow pattern and the air flow properties within the room. These data are intended for use in the evaluation of the existing numerical and scale models, and to aid in furthering the understanding of the behaviour of room ventilation airflows.     

Long-term field survey on thermal adaptation in office buildings in Japan

A long-term field survey was conducted with six buildings in order to investigate how the occupants adapt to the indoor climate in office buildings in Japan. More than 5000 questionnaires and corresponding indoor temperatures were collected. Clothing adjustment was observed to be related to outdoor temperature and indoor temperature, as well as dress codes. No considerable differences were found on the thermal perceptions between two groups of buildings, which provided different levels of opportunity for controlling indoor climate. With both groups, the preferred SET* was always close to 26 °C. The comfort temperature was estimated from the results of clothing adjustment and the preferred SET*. The gradient of the comfort temperature to outdoor temperature was found to be between the adaptive model for centralized HVAC and for natural ventilation. It could be caused by that the major part of the occupants in the present study had more opportunity to control their thermal conditions than in the centralized HVAC buildings (i.e. operable windows, controllable HVAC or personal fans).     

Toxicity of chlorine to juvenile spot, Leiostomus Xanthurus

The sensitivity of juvenile spot, Leiostomus xanthurus, to total residual chlorine (TRC) in flowing sea-water was investigated. Incipient LC₅₀ bioassays, histopathology, avoidance tests and the combined effect of thermal stress and TRC were used to assess sensitivity.

Estimated incipient LC₅₀ values were 0.12 mg 1⁻¹ TRC at 10°C and 0.06 mg 1⁻¹ TRC at 15°C. Histological examination of spot used in the incipient LC₅₀ bioassay at 15°C and sacrificed while alive indicated pseudobranch and gill damage occurred in individuals exposed to a measured TRC concentration of 1.57 mg 1⁻¹. Spot exposed to lower concentrations of TRC, 0.02 0.06 mg 1⁻¹ at 15°C and sacrificed alive showed no consistent tissue damage.

Spot demonstrated temperature dependent avoidance responses to TRC. At 10°C, a concentration of 0.18 mg 1⁻¹ was required for significant (X²; P < 0.05) avoidance; at 15 and 20°C, spot showed significant avoidance of TRC concentrations as low as 0.05 mg 1⁻¹.

Simultaneous exposure of spot to thermal stress (5, 10 or 13°C above the acclimation temperature of 15°C) at measured TRC concentrations of 0.05 0.07 and 0.34–0.52 mg 1⁻¹ demonstrated a significant, (Z²) with Yates correction, P < 0.05) increase in sensitivity to TRC with increased temperature and exposure times for some of the groups tested.     

Assessing thermal comfort of active people in transitional spaces in presence of air movement

The aim of this study is to develop a modeling methodology to assess thermal comfort and sensation of active people in transitional spaces and consider how comfort can be achieved by air movement while changing upper body clothing properties. The modeling is based on a bioheat model, capable of predicting segmental skin and core temperature from locally ventilated clothed body parts. The bioheat model is integrated with thermal comfort and sensation models to predict comfort in presence of air movement.The model accuracy in predicting comfort was validated by and agreed with the results of a survey administered to subjects wearing typical clothing at different activity levels to record their overall and local thermal sensation and comfort in a transitional space at Beirut summer climate. The transitional space temperature monitored during the experiments ranged between 27 °C and 30 °C.A parametric study is performed to assess thermal comfort in transitional spaces for different air movement levels and for three clothing designs. The high permeable clothing at 1.5 m/s and indoor temperature of 30 °C improved the Predicted Mean Vote to values less than 0.5 compared to 1.01 attained with typical low permeable clothing.     

考虑应力路径的软黏土小应变特性试验研究

以苏南地区原状软黏土经K₀固结形成的试样为对象,利用配备了弯曲元系统和局部位移测量系统的GDS应力路径三轴测试系统,研究了小应变范围内应力路径转角θ对剪切模量衰减曲线以及阈值剪应变(γ_0.7)的影响。试验结果表明,土体的初始剪切模量G₀值与初始固结应力大小呈正相关关系,并可表示为与孔隙比e、平均有效应力p′相关的函数关系式。土体的剪切模量在10^-6~10^-3的应变范围内随着剪应变的增加而逐渐衰减,并表现出和试验应力路径与近期应力历史间夹角θ的相关性:应力路径对衰减曲线的影响随着应力路径转角θ的增大逐渐增大,当两者完全相反时,其影响最大。在K₀固结条件下,应力路径转角θ对γ_0.7的影响大于初始固结平均有效应力p′,同时γ_0.7值随着应力路径转角θ的增大而逐渐增大。     

花岗岩力学特性温度效应的试验研究

利用MTS815岩石力学试验系统完成了不同温度下的20个花岗岩试样的三轴压缩试验。分析了温度对花岗岩试样的强度特性、变形特性以及破坏特征的影响,能够在实际工程中起到一定的指导作用。试验结果表明:在20 ℃到40 ℃的范围,弹性模量随温度升高而降低,泊松比随温度升高而升高,且变化幅度都较大,但当温度超过40 ℃以后,随温度升高的变化幅度明显降低;随着温度的升高,峰值强度逐渐降低,而且温度对峰值强度的影响随着围压的增加而减弱;内聚力c值随温度升高而降低,内摩擦角φ值随温度升高有升高的趋势,抗剪强度τ_f大致呈线性减小的关系,且随着正应力的升高,温度对花岗岩抗剪强度的影响有减弱的趋势;花岗岩的变形破坏特征在一般条件下表现为典型的弹脆性体特征,但是在较高围压和较高的温度耦合作用下表现为弹塑性变形-累进性破裂-脆性破坏的特征。     

Influence of temperature and substrate shocks on survival and succinic dehydrogenase activity of heterotrophic freshwater bacteria

The influence of temperature shocks on aquatic bacteria was studied in laboratory experiments with regard to population shifts in lake water communities of aerobic heterotrophic bacteria including coliforms. as well as in synthetic mixed cultures of psychrotolerant aquatic isolates. In addition, succinic dehydrogenase activity was used as a parameter of bioactivity. Each experiment was designed to study concomitant effects of elevated levels of organic substrates.

Simultaneous additions of complex nutrients such as 100–300 mg 1⁻¹ of meat peptone to lake water caused a synergistic action of substrate and temperature on population dynamics by depressing population densities at temperatures below 20°C. In contrast, stimulation was observed at higher temperatures particularly for the coliform group. In mixed cultures consisting of Cytophaga, Chromobacterium and Arthrobacter as important members of the heterotrophic microflora of the investigated lake water, substrate accelerated death was induced by temperature shocks beyond the maximum growth temperatures. The succinic dehydrogenase activity of a psychrotolerant strain of Cytophaga failed to show more sensitive responses to temperature shocks than did viable counts.     

The potentials of lateritic soil—Clay and clay-sand mixes in the manufacturing of bricks for masonry units

Bricks were manufactured from lateritic soil-clay and clay-sand mixes with various mix proportions; 30, 40, 50, and 60% sand (by weight) were mixed with clay soil, 20 and 40% clay (by weight) were mixed with lateritic soil. The bricks were burnt at 1000°C for periods of 2, 4 and 6 h. Various properties of the bricks such as linear shrinkage, density, compressive strength and water absorption were measured. Test results showed that the addition of 40% clay in lateritic soil was the optimum for the production of bricks from lateritic soil. The addition of 30% sand in clay was optimum for the production of bricks from clay. The compressive strength of the investigated bricks was also compared with British starutory requirements for the minimum compressive strengths in bricks for various walls. The comparison showed that both lateritic soil-clay and clay-sand mixed bricks could be used in load bearing walls.     

Thermal effect of temperature gradient in a field environment chamber served by displacement ventilation system in the tropics

The effect of vertical air temperature gradient on overall and local thermal comfort at different overall thermal sensations and room air temperatures (at 0.6 m height) was investigated in a room served by displacement ventilation system. Sixty tropically acclimatized subjects performed sedentary office work for a period of 3 h during each session of the experiment. Nominal vertical air temperature gradients between 0.1 and 1.1 m heights were 1, 3 and 5 K/m while nominal room air temperatures at 0.6 m height were 20, 23 and 26 °C. Air velocity in the space near the subjects was kept at below 0.2 m/s. Relative humidity at 0.6 m height was maintained at 50%. It was found that temperature gradient had different influences on thermal comfort at different overall thermal sensations. At overall thermal sensation close to neutral, only when room air temperature was substantially low, such as 20 °C, percentage dissatisfied of overall body increased with the increase of temperature gradient. At overall cold and slightly warm sensations, percentage dissatisfied of overall body was non-significantly affected by temperature gradient. Overall thermal sensation had significant impact on overall thermal comfort. Local thermal comfort of body segment was affected by both overall and local thermal sensations.     

Sequential inactivation of Cryptosporidium parvum using ozone and chlorine.

Inactivation of bovine-derived C. parvum oocysts was studied at bench-scale in oxidant demand free 0.05 M phosphate buffer using free chlorine alone or ozone followed by free chlorine at temperatures of 1°C, 10°C and 22°C at pH 6. Animal infectivity using neonatal CD-1 mice was used for evaluation of oocyst viability after treatment. Kinetic models based on the linear Chick–Watson model were developed for free chlorine inactivation and ozone/free chlorine sequential inactivation for 0.4 or 1.6 log-units of ozone primary kill. At 22°C, ozone pre-treatment increased the efficacy of free chlorine for about 4–6 times depending on the level of ozone primary kills. Gross kills of the ozone/free chlorine sequential inactivation were a function of ozone primary kills and increased linearly with the free chlorine C_avgt (arithmetic average of the initial and final residual×contact time) product. Temperature was critical for both single and sequential inactivation, and the efficacy of free chlorine after 1.6 log-units of ozone primary inactivation decreased by a factor of 1.8 for every 10°C temperature decrease. Given an ozone primary kill of 1.6 log-units, the free chlorine C_avgt products required for a gross kill of 3.0 log-units were 1000, 2000 and 3300 mg min/L for 22°C, 10°C and 1°C, respectively.