共查询到20条相似文献,搜索用时 15 毫秒
1.
During a fire, concrete is submitted to very high temperatures which can lead to structural collapse. The aim of this research is to study the behaviour of mortar specimens made of Portland cement and ground granulated blast furnace slag (GGBFS) which are heated to 900?°C. The samples are submitted to compressive and flexural strength tests and the microstructure is analysed by thermogravimetric analysis (TG and DTA), analysis and mercury intrusion porosimetry. The results indicate that a substitution rate of Portland cement by GGBFS of over 50?% gives residual compressive strengths that, after heating to 600?°C, are close to initial strengths before heating. The greater quantities of bound water, an acceleration of the hydration process due to heating and a lower porosity for specimens with GGBFS explain this increase. At 900?°C, the strong degradation of the microstructure results in strengths of less than 20?% of the initial strengths for specimens with or without GGBFS. Also, after cooling, the GGBFS reduces lime rehydration because of the decomposition of the portlandite between 450 and 550?°C, thus avoiding the risk of concrete cracking. 相似文献
2.
A study on durability properties of high-performance concretes incorporating high replacement levels of slag 总被引:2,自引:1,他引:1
This paper presents an experimental study of combined effects of curing method and high replacement levels of blast furnace
slag on the mechanical and durability properties of high performance concrete. Two different curing methods were simulated
as follows: wet cured (in water) and air cured (at 20°C and 65% RH). The concretes with slag were produced by partial substitution
of cement with slag at varying amounts of 50–80%. The water to cementitious material ratio was maintained at 0.40 for all
mixes. Properties that include compressive and splitting tensile strengths, water absorption by total immersion and by capillary
rise, chloride penetration, and resistance of concrete against damage due to corrosion of the embedded reinforcement were
measured at different ages up to 90 days. It was found that the incorporation of slag at 50% and above-replacement levels
caused a reduction in strength, especially for the early age of air cured specimens. However, the strength increases with
the presence of slag up to 60% replacement for the 90 day wet cured specimens. Test results also indicated that curing condition
and replacement level had significant effects on the durability characteristics; in particular the most prominent effects
were observed on slag blended cement concrete, which performed extremely well when the amount of slag used in the mixture
increased up to 80%. 相似文献
3.
Tu-Cheng Hung Jong-Shin Huang Yi-Wen Wang Ya-Chu Fan 《Journal of Materials Science》2013,48(21):7446-7455
A mixture of 70 % metakaolin and 30 % blast furnace slag powders, employed as the raw material, is mixed with different alkaline activating solutions in the production of metakaolin-based inorganic polymer foams (MIPF) with various densities ranging from 0.4 to 1.0 g/cm3 using a mechanical foaming process. The microstructures of metakaolin and slag powders, inorganic binder, and MIPF specimens are characterized by using XRD, FTIR, and image analyses. The effects of stirring time, water/binder ratio, and foaming agent on the properties of inorganic binders are also evaluated. Moreover, the pore size distributions, thermal and mechanical properties of the MIPF specimens are obtained by conducting a series of measurements and then compared with each other. Based on the experimental results, it is found that the measured cell length, cell wall thickness, compressive strength, flexural strength, and coefficient of thermal conductivity of the MIPF specimens are significantly affected by their densities. 相似文献
4.
Compressive strength and microstructure of alkali-activated fly ash/slag binders at high temperature
This paper reports the results of the compressive strength and microstructure of various alkali-activated binders at elevated temperatures of 300 and 600 °C. The binders were prepared by alkali-activated low calcium fly ash/ground granulated blast-furnace slag at ratios of 100/0, 50/50, 10/90 and 0/100 wt.%. Specimens free of loading were heated to a pre-fixed temperature by keeping the furnace temperature constant until the specimens reached a steady state. Then the specimen was loaded to failure while hot. XRD, SEM and FTIR techniques were used to investigate the microstructural changes after the thermal exposure. The fly ash-based specimen shows an increase in strength at 600 °C. On the other hand, the slag-based specimen gives the worst high-temperature performance particularly at a temperature of 300 °C as compared to ordinary Portland cement binder. This contrasting behaviour of binders is due to their different binder formulation which gives rise to various phase transformations at elevated temperatures. The effects of these transformations on the compressive strength are discussed on the basis of experimental results. 相似文献
5.
《Materials Science & Technology》2013,29(12):986-992
AbstractDepths of carbonation on specimens of concretes aged for up to 10 years are compared. Both good and poor curing conditions, with either indoor or outdoor exposure are considered. It is demonstrated that the carbonation depth is related systematically to the standard cube strength in dense concretes containing up to and including 40% replacement of Portland cement by pulverized fuel ash (PFA) or up to and including 60% by ground granulated blast furnace slag (GGBFS) or ground pelletized blast furnace slag (GPBFS). The main implications of these findings to methods of specifying concrete (BS 5328: 1981) are that designed mixes may give higher rates of carbonation for low-heat Portland blast furnace cement, but not for other permitted cement replacements, and that prescribed mixes will usually give higher rates if Portland cement is partially replaced by any permitted quantity of cement replacement. Depths of carbonation in concrete containing porous aggregate are more closely related to total water/cement ratio than to standard cube strength. This is probably a result of a closer relationship between total water/cement ratio and pore structure, which controls the rate of carbonation. A comparison has been made between concretes containing porous aggregate and those containing cement replacements by introducing an efficiency factor (k) for cement replacements similar but not always identical to the cementing efficiency factor.MST/690 相似文献
6.
Portland cement blended with waste products such as blast furnace slag and fly ash are frequently used to create more sustainable concrete, but their nanoscale mechanical behavior, particularly after thermal damage, has not been well-studied. Here, nanoindentation experiments confirm that concrete produced with blended cements contains hydration products with nearly identical nanoscale mechanical properties to the hydration products found in concretes produced with ordinary Portland cement. The volume fractions of the hydration products, particularly calcium-silicate-hydrate (C-S-H) phases, are formed in different proportions with the addition of fly ash and blast furnace slag. After exposure to fire damage, the nanoscale behavior of concretes produced with fly ash and slag also matches the nanoscale behavior of conventional concretes. This suggests that any macroscopic differences between fire damage behavior of blended cement concrete and ordinary Portland cement concrete must have origins in a larger length scale. 相似文献
7.
This paper presents the results of an experimental investigation carried out to study the effect of granulated blast furnace slag and two types of superplasticizers on the properties of self-compacting concrete (SCC). In control SCC, cement was replaced with 10%, 15%, 20%, and 25% of blast furnace slag. Two types of superplasticizers: polycarboxylate based superplasticizer and naphthalene sulphonate based superplasticizers were used. Tests were conducted for slump flow, the modified slump test, V-Funnel, J-Ring, U-Box, and compressive strength. The results showed that polycarboxylate based superplasticizer concrete mixes give more workability and higher compressive strength, at all ages, than those with naphthalene sulphonate based superplasticizer. Inclusion of blast furnace slag by substitution to cement was found to be very beneficial to fresh self-compacting concrete. An improvement of workability was observed up to 20% of slag content with an optimum content of 15%. Workability retention of about 45 min with 15% and 20% of slag content was obtained using a polycarboxylate based superplasticizer; compressive strength decreased with the increase in slag content, as occurs for vibrated concrete, although at later ages the differences were small. 相似文献
8.
This paper presents a study on the effect of temperature exposure of binders of blast furnace slag (BFS) and metakaolin (MK) in BFS-MK weight ratios of 100-0, 50-50, and 0-100 activated with sodium silicate of modulus Ms = SiO2/Na2O = 1 and 5, 10 and 15% Na2O. A blended ordinary CPC-30R Portland cement reference was used. Pastes were subjected to exposure up to 1200 °C and the performance was evaluated in terms of compressive strength, residual strength, volumetric shrinkage, physical appearance and microstructural changes at different temperatures. All the binders retained more than 30 MPa after exposure to 800 °C for 4 h; specimens of MK and CPC-30R experienced the highest strength losses of 42 and 56% respectively, while those of 100-0 and 50-50 showed minor losses of ∼20%. After heating at 1200 °C the samples showed microstructural damage and more than 65% of strength losses. XRD indicated that the 100-0 and 50/50 binders are prone to form crystalline phases as akermanite, nepheline and nosean at temperatures greater than 1000 °C, while 0-100 geopolymeric binders preserved mostly an amorphous structure even at 1200 °C with some traces of mullite. The dehydration of C-A-S-H and N-A-S-H altogether with the crystallization of the binder gel induced the formation of highly porous microstructures. 相似文献
9.
Tongsheng Zhang Qijun Yu Jiangxiong Wei Pingping Zhang 《Cement and Concrete Composites》2012,34(5):692-699
To achieve sustainable development of cement industry, cementitious efficiency of different cement clinker and supplementary cementitious materials (SCMs) fractions, in terms of hydration process and strength contribution ratio, was characterized. The results show that blast furnace slag and steel slag should preferably be arranged in fine fractions due to their desirable hydration processes and high strength contribution ratios. Cement clinker should be positioned in intermediate fraction (8–24 μm) due to its proper hydration process. Replacement of cement clinker by SCMs with low activity or inert fillers in coarse fractions was also suggested, because coarse cement clinker fractions gave very low hydration degrees and little strength contribution. Both early and late properties of gap-graded blended cements prepared can be comparable with or higher than those of Portland cement, indicating both cement clinker and SCMs were used more efficiently. These blended cements also give additional cost savings and reduced environmental impact. 相似文献
10.
Ultra low and negative expansion glass-ceramic materials produced from pyrophyllite and blast furnace slag 总被引:1,自引:0,他引:1
Ultra low and negative expansion glass-ceramic materials have been obtained from pyrophyllite and blast furnace slag. The
batch composition was modified with the addition of lithium carbonate, hydrated alumina, boric acid and nucleating agent (titania).
The batch was melted at 1400°C followed by casting in the form of bars and annealed at 510°C for 4 h. The annealed specimens
were subjected to heat treatment at predetermined temperatures selected from DTA study of the parent glass. Thermal expansion
measurement and X-ray diffraction analysis revealed that the specimen nucleated at 545°C for 4 h and crystallized at 720°C
for 2 h which resulted in negative coefficient of thermal expansion [(-) 9 to (-) 2 x 10-7/°C] over the temperature range (30-600°C) due to the formation ofβ bd-eucryptite while other heating schedule showed the formation of spodumene and lithium aluminium silicates. The samples
showed excellent flexural strength value and varied in the range 120–200 MPa depending upon the phases present. 相似文献
11.
M. Sugiura A. Shinotake M. Nakashima N. Omoto 《International Journal of Thermophysics》2014,35(6-7):1320-1329
As the initial process in an integrated steel-making plant, molten iron is produced in a blast furnace. The molten iron has a temperature between 1700 K and 1900 K. The outflow stream discharged from a taphole comprises the molten iron and slag (which is a mixture of molten oxides). Monitoring of the stream temperature is important because it has information on the thermal condition inside the blast furnace. A newly developed simultaneous measurement technique for temperature and iron–slag ratio is reported. A monochromatic CCD camera with a short exposure time is used to obtain a thermal image of the rapidly moving stream. The thermal image has a marble-like pattern caused by the physical separation of the iron and slag and their different optical properties. Iron thermometry is realized by automatically detecting the peak of the iron gray-level distribution on a histogram. Meanwhile, the thermal radiance of the semitransparent slag varies as a function of the thickness. The slag temperature is calculated from the maximum gray level, presuming that the emissivity of the slag is constant at a thick slag part. The slag ratio is measured by counting the number of pixels on the histogram. A field test was carried out at an operating blast furnace. The iron temperature, slag temperature, and slag ratio were successfully measured. This multiple image measurement is expected to be the new information source for stable blast furnace operation. 相似文献
12.
以冶金废渣钢渣、矿渣及电厂废渣脱硫石膏为主要原材料,添加少量的硅酸盐水泥及激发剂,制备了一种新型的钢渣~矿渣基全尾矿充填胶结材料。通过系统试验,确定了制备钢渣-矿渣基全尾矿充填胶结材料的最优配比及影响其性能的显著性因素。结果表明,采用钢渣-矿渣基全尾矿充填胶结材料制备的充填体在胶砂比为1;9、固体浓度约为68%时,28天抗压强度可达到2.5MPa以上。钢渣-矿渣基全尾矿充填胶结材料的固体废弃物含量高达90%以上,且成本明显低于普通水泥,因此会产生较好的环境和经济效益。 相似文献
13.
E. A. Teymurova M. M. Akhmedov M. R. Manafov I. G. Melikova 《Materialwissenschaft und Werkstofftechnik》2012,43(3):212-219
This article is dedicated to the investigations of the individual complex processing of the high ferriferrous sulphide lead concentrates by the way of lead blast furnace reducing melting. The data of the trials series of high ferriferrous lead sinters' reduction melting with the operating blast furnace have been presented. The results of investigations indicate that low lead losses with the slag (1.4÷1.8 wt.‐%) can be achieved by maintaining a slag composition of 38.4÷41.1 wt.‐% FeO and 0.70÷0.74 CaO/SiO2 ratio, with a lead sinter throughput – 55÷60 tonnes/m2 · day. The slag liquidus temperature is estimated to be ?1170°C. 相似文献
14.
Properties of self-compacting portland pozzolana and limestone blended cement concretes containing different replacement levels of slag 总被引:1,自引:0,他引:1
In order to reduce energy consumption and CO2 emission, and increase production, cement manufacturers are blending or inter-grinding mineral additives such as slag, natural
pozzolana, and limestone. This paper reports on the results of an experimental study on the production of self-compacting
concrete (SCC) produced with portland cement (PC), portland pozzolana (PPC) and portland limestone (PLC) blended cements.
Moreover, the effect of different replacement levels (0–45%) of ground granulated blast furnace slag (GGBFS) with the PPC,
PLC, and PC cements on fresh properties (such as slump flow diameter, T
500 slump flow time, V-funnel flow time, L-box height ratio, setting time, and viscosity) and hardened properties (such as compressive
strength and ultrasonic pulse velocity) of self-compacting concretes are investigated. From the test results, it was found
that it was possible to manufacture self-compacting concretes with PPC or PLC cements with comparable or superior performance
to that of PC cement. Furthermore, the use of GGBFS in plain and especially blended cement self-compacting concrete production
considerably enhanced the fresh characteristics of SCCs. 相似文献
15.
Residual strength properties of sodium silicate alkali activated slag paste exposed to elevated temperatures 总被引:1,自引:0,他引:1
The residual compressive strength behavior of alkali activated slag paste (AASP) after temperature exposures up to 1,200°C
was investigated. Strength loss of approximately 60% occurred between 100 and 200°C and a further strength loss in the order
of 30% at 800°C. Total loss of strength occurred at 1,200°C. Thermogravimetric studies (TGA/DTG) verified AASP contained no
Ca(OH)2 which governs the chemical mechanism of strength loss for ordinary Portland cement (OPC) and blended slag cement pastes.
However, the TGA results showed that AASP had a higher water loss than the other binders between 100 and 200°C and higher
thermal shrinkage as indicated by the dilatometry studies. The high thermal shrinkage led to a differential thermal shrinkage
gradient within the AASP and induced micro stresses and cracking which was more prominent for larger samples. Differential
thermal shrinkage caused by the higher thermal shrinkage of the AAS material was concluded as the mechanism which gives lower
residual strength in AASP compared to OPCP. 相似文献
16.
17.
In this paper, the studies concern the influence that different fillers have on the properties of SCC of different strength
classes when exposed to high temperatures. A total of six different SCC and two conventional concrete mixtures were produced.
The specimens produced are placed at the age of 180 days in an electrical furnace which is capable of reaching 300°C at half
an hour and 600°C at 70 min. The maximum temperature is maintained for an hour. Then the specimens are let to cool down in
the furnace. The hardened properties measured after fire exposures are the compressive strength, splitting tensile strength,
water capillary absorption and the ultrasonic pulse velocity. Explosive spalling occurred in most cases when specimens of
higher strength class are exposed to high temperatures. The spalling tendency is increased for specimens of higher strength
class C30/37 irrespective of the mixture type (SCC or NC) and the type of filler used. 相似文献
18.
Experiments were conducted on 150 × 600 mm cylindrical specimens to investigate creep and drying shrinkage of concrete containing ground granulated blast furnace slag (GGBFS). The creep strain was measured for 150 days under a constant sustained load. The creep strain recovery was measured for one subsequent month after the removal of the sustained load. The shrinkage strain was also measured for 180 days. The amount of cement replacement by GGBFS was 20%, 40% and 60% by weight of cement. The test results indicate that higher GGBFS percentage exhibits higher creep and shrinkage strains. At 150 days of sustained loading, the average creep coefficients of 20%, 40% and 60% GGBFS concrete are 16.3%, 33.3% and 55.2% higher than plain concrete. In the absence of a creep and shrinkage prediction model for GGBFS concrete, a modification factor is suggested for incorporating the effect of GGBFS proportion in the existing models. The available models for predicting creep and shrinkage strain of plain concrete are compared. 相似文献
19.
Pelletization is a worldwide process used in producing artificial aggregates although its usage is not common in Turkey. In this study, lightweight aggregates (LWAs) were manufactured through cold-bonding pelletization of ground granulated blast furnace slag (G) and two types of fly ash with different finenesses (Fly ash A and B). Ordinary Portland cement (PC) was used as a binder at varying amounts from 5 to 20 % by weight. A total of 20 cold-bonded lightweight aggregates were produced at room temperature with different combinations of PC, FA and/or G. The hardened aggregates were tested for specific gravity, water absorption, and crushing strength. Thereafter, lightweight concretes (LWCs) were produced with water to cement ratio of 0.50 and a cement content of 400?kg/m3 by using such lightweight aggregates. The hardened concretes were tested for compressive strength at 28 and 56?days to explore the effect of aggregate types on the compressive strength development. Test results revealed that the amount of cement content had a significant effect on the strength of LWAs which in turn governed the variation in compressive strength of the LWCs. The highest 28 and 56-day compressive strengths of 43 and 51?MPa, respectively were achieved for the concretes including LWAs produced from the blend of 40 % slag, 40 % FA-A and 20 % PC. 相似文献
20.
将水泥、粉煤灰和磨细高炉矿渣作为保水材料灌注于多孔水泥混凝土母体中,形成具有保水降温功能的铺面材料。分别提供了多孔水泥混凝土母体和保水材料的设计方法,并成型试件对保水铺面水泥混凝土材料的强度、降温效果和抗冻性进行了测试。实验结果表明设计的多孔水泥混凝土母体和保水材料均满足施工和功能要求,成型的保水降温功能水泥混凝土试件28d抗压强度和抗折强度分别能够达到27.7和38.2MPa;在最高气温为33℃的测试条件下,其表面最高温度比普通水泥混凝土降温7℃左右,但随着水分的减少降温效果变差;此外,冻融后保水降温水泥混凝土抗压强度会下降,但不明显。 相似文献