建筑工程英文原文及翻译
委婉拒绝Effect of Water Content on the Properties of Lightweight Alkali-Activated Slag Concrete
Keun-Hyeok Yang ，Ju-Hyun Mun ，Jae-Il Simand Jin-Kyu Song
Keyword ：concrete 、water content
Introduction
With the gradual growth of a global effort to reduce greenhou gas emissions, a large ction of the concrete industry has growing interest in minimizing the u of ordinary portland cement (OPC).
This is becau it is estimated that the production of 1 t of OPC requires about 2.8 t of raw materials, such as limestone and coal, and releas about 0.7 t of carbon dioxide (CO 2) to the earth’s atmosphere
from the decarbonation of lime in the kiln (Gartner 200466
)
. As a result, since the late 1980s, toward the reduction of the u of OPC, various investigations have been conducted in veral fields to develop a cementless alkali-activated (AA) ground granulated blast furnace slag binder together with a fly
ash ash––bad geopolymer binder. As pointed out by Shi et al. (20061111
), AA slag binders and concrete will gradually attract a great deal of interest becau of their extensive advantages of lower carbon
emissions and energy cost, higher-strength development, and better durability than with OPC concrete. In particular, AA slag concrete can effectively be applied to precast concrete products.
It is generally estimated that the amount of CO 2 emitted from the consumption of fossil fuels for 设计总监
commercial and residential heating accounts for approximately 12% of the total CO 2 emissions into the earth’s atmosphere. In addition, the nonnegligible amounts of CO 2 are emitted from buildings or factory cooling. As a result, the development of energy saving systems and new and renewable energy
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sources has become one of the hottest issues in building structures. The u of lightweight concrete as a building material is highly effective for saving energy becau of the enhanced thermal insulation capacity through the lower thermal conductivity of lightweight aggregates. In addition, the application of structural lightweight concrete has veral advantages as the reduction of the dead load becau a lower density of concrete allows for smaller and lighter weight structural member that can lead to more available space and improves the ismic resistance capacity of the upper structures.
Furthermore, the smaller and lighter elements of precast concrete members are preferred to make the handling and transporting system less expensive. 此北固山下
Synergy effects are expected when AA slag binder and lightweight aggregates are combined to produce environmentally friendly concrete becau of the various advantages of both materials. One of the most significant effects is the highly reduced CO 2 emission from concrete building structures by the u of AA slag binder with a lower CO 2 emission and an energy-saving effect owing to the u of
lightweight aggregates. In addition, precast concrete can be produced with good quality and
economical efficiency from an early higher strength development capacity of AA slag paste and a lower density of aggregates. However, the available experimental data (Collins and Sanjayan 19995
; Yang et al. 200917) needed to determine a reliable mixing design and the mechanical properties of lightweight AA slag concrete are very rare. Unlike normal-weight OPC concrete, the workability and development of compressive strength of lightweight AA slag concrete is very nsitive to the hydration rate of the binder, the physical properties of lightweight aggregates, and the mixing conditions, such as the water
content, water-binder ratio, and the proportion of lightweight aggregates. Yang et al. (20091717) showed that the initial slump and the slump loss of AA slag concrete are significantly affected by the
water-binder ratio and lightweight aggregate proportions caud by the high water absorption capacity
of lightweight aggregates. Collins and Sanjayan (199955
)
also pointed out that the internal curing effect on the slump loss and the shrinkage of concrete is strongly dependent on the state of moisture in lightweight aggregates and water content. In addition, a quicker slump loss is generally obrved in lean AA slag concrete mixes than in OPC concrete becau of the fast chemical reaction between various alumino-silicate oxides with silicate and/or the formation of silica-rich calcium silicate hydrates gel (Shi et al. 200611
). Therefore, the water content and lightweight aggregate proportions need to be significantly managed for realizing the targeted slump and retarding the slump loss of lightweight AA slag concrete.
In the prent study, five all-lightweight and five sand-lightweight AA slag concrete mixes were
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tested to evaluate the effect of the water content on the workability, mechanical properties, and shrinkage strain of the concrete. The rate of compressive strength development and the shrinkage strain were measured and compared with the empirical models propod by American Concrete
Institute (ACI) 209 (ACI 199411) for normal-weight portland cement concrete. To examine the practical applicability of the lightweight AA slag concrete, the splitting tensile strength and the moduli of elasticity and rupture recorded from the concrete specimens were compared with the values predicted through various sources for lightweight OPC concrete, whenever possible. The sources included design equations specified in ACI 318-08 or Eurocode 2 [British Standards Institution empirical equations
propod by Slate et al., and a databa compiled by Sim and Yang.
Experimental Details Materials
Ground granulated blast furnace slag (GGBS) was activated by sodium silicate (Na 2O·O·SiO
SiO 2) and calcium hydroxide [Ca(OH)2] powders and ud as a cementitious binder. The GGBS ud for the source material had a high CaO content and SiO 2-to-Al 2O 3 ratio by mass of 2.29. The specific gravity and specific surface area measured for the GGBS were 2.2 and 4,200 cm 2/g, respectively. The
2O) and 45% silicon oxide sodium silicate powder ud was a compound of 50.2% sodium oxide (Na
(SiO2), producing a molar ratio (SiO2/Na2O) of 0.9. The purity of the Ca(OH)
2 powder ud was 95.8%. Wang et al. showed that a higher strength of AA GGBS concrete was obtained by using liquid
16, 201015) also recommended that the sodium silicate with a molar ratio of 1 to 1.5. Yang et al. (2008
ratios by weight of Ca(OH)2 to the binder, including the GGBS and alkali activators, and of Na
2O in
sodium silicate to GGBS were above 7.5% and 3%, respectively, to facilitate the chemical reaction by ion exchange between the silicate anions of the GGBS and the cations of the alkaline activators. Therefore, the Ca(OH)2-to-binder ratio was lected to be 7.5% and sodium silicate was added so that the Na2O-to-GGBS ratio would be 3% to produce a cementless AA slag binder.
Artificially expanded clay granules with maximum sizes of 19 mm and 5 mm were ud for li拔罐拔出水泡是好是坏
ghtweight coar and fine aggregates, respectively. Locally available natural sand with a maximum particle size of 5 mm was also ud for normal-weight fine aggregates. From X-ray diffraction measurements, the main composition of the lightweight aggregates was quartz and calcium aluminum silicate. Fig. 1 shows that the lightweight aggregates were spherical in the shape and had a clod surface with a slightly rough texture. The core of the particle had a uniformly fine and porous structure that led to high thermal and acoustic insulation but induced high water absorption and low strength. In particular, the rate of water absorption of lightweight aggregates was extremely fast for the lightweight
2. The aggregates during the first 3 h, and then the absorption rate slowed down, as shown in Fig.
specific gravity of the lightweight aggregates ud was approximately 2.5 times lower than that of natural sand. The particle distribution of lightweight aggregates showed a continuous grading that satisfied the standard distribution curves recommended in the Korea Industrial Standard (Korean Standards Information Center 20068) specification, as plotted in
Fig 1.
Shape and scanning electron microscope (SEM) images of the lightweight coar aggregate ud
Fig 2.
Water absorption rates of the aggregates ud
Fig 3.
Particle distribution curves of the aggregates ud: (a) lightweight aggregates; (b) normal-weight aggregates (natural sand)
Mix Proportions
Five all-lightweight and five sand-lightweight AA slag concrete mixes were prepared by varying the
2. Higher water-binder ratios can result in water content per unit volume of concrete, as given in Table
2). In addition, the compressive strength of lightweight gregation in the lightweight concrete (ACI 1998
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AA slag concrete targeted in the prent study was above 24 MPa for application to structural concrete members. From various preliminary tests, the water-binder ratio by weight and fine aggregate-to-total
aggregate ratio by volume were fixed at 30% and 40%, respectively, in all concrete mixes. The mixture proportions of all the concrete specimens were determined on the basis of the weight method propod by ACI 211.
Mixing, Curing, and Testing
Lightweight aggregates and natural sand were dampened for 24 h and then air-dried for another 24 h to
simulate the saturated surface dried-state that is commonly employed in ready-mixed concrete plants. The alkaline binder and aggregates were dry-mixed in a pan mixer for 1 min, then water was added and mixed for another 1 min. For all the concrete mixes, a polycarbonate-bad water-reducing admixture with an air-entraining agent was added by 0.5% relative to the amount of binder ud. After the initial slump was tested, each mix was poured into various steel molds to measure the compressive strengths and other mechanical properties. Immediately after casting, all specimens were cured at room temperature until testing at the specified ages.
Test Results and Discussions
Initial Slump and Slump Loss
The initial slump, S i, of the lightweight AA slag concrete incread with the increa of water
99). At the content, which is generally obrved in the lightweight OPC concrete as well (Neville 1995
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same water content, the all-lightweight AA slag concrete showed a higher value of initial slump than the
