采用X-射线衍射(X-ray diffraction,XRD)、热重-差热扫描分析(TG-DSC)、扫描电子显微镜(scanning electron microscope,SEM)等方法对不同水化龄期掺4%速凝剂水泥净浆微观结构进行分析。结果表明:速凝剂的掺入显著影响水泥水化进程。在水...采用X-射线衍射(X-ray diffraction,XRD)、热重-差热扫描分析(TG-DSC)、扫描电子显微镜(scanning electron microscope,SEM)等方法对不同水化龄期掺4%速凝剂水泥净浆微观结构进行分析。结果表明:速凝剂的掺入显著影响水泥水化进程。在水泥-速凝剂-水体系中,Na Al O2及Na2CO3令石膏缓凝作用失效,铝酸三钙快速水化生成水化铝酸钙晶体,并与钙矾石及钠长石晶体形成相互攀附的网络结构对水泥颗粒产生"桥连"作用而实现速凝。同时,大量水化热促进水泥熟料矿物水化速率加快,净浆密实度快速增加。同时,随着水化龄期延长,净浆物相组成、钙矾石及氢氧化钙含量发生显著变化。展开更多
Circulating fluidized bed combustion （CFBC） ash can be potentially used as supplementary cementitious materials for concrete production due to its desirable pozzolanic activity. The adsorption properties of CFBC ash...Circulating fluidized bed combustion （CFBC） ash can be potentially used as supplementary cementitious materials for concrete production due to its desirable pozzolanic activity. The adsorption properties of CFBC ash-cement pastes were studied, and ordinary pulverized coal combustion （PCC） fly ash-cement pastes were used as control. The water-adsorption and superplasticizer （SP）-adsorption properties of the pastes were evaluated by water demand and UV-visible absorption spectroscopy respectively. The results show that CFBC ash-cement system has greater compressive strength as compared with PCC fly ash-cement system at a given curing age, although the water demand of the former is significantly higher than that of the latter. CFBC ash-cement pastes possess higher adsorption ability of aliphatic SP than PCC fly ash-cement pastes and the adsorption amount increases with an increase in ash replacement ratio. CFBC ash- cement pastes exhibit lower workability with higher slump loss. It is concluded that CFBC ash can be potentially used as supplementary cementitious material in concrete production, but the mix design of CFBC ash concrete needs to be appropriately adjusted. It is suggested that CFBC ash is used for the production of the concrete needing low flowability.展开更多
Reuse of concrete waste, especially in large quantity, can save not only material but also cost for its disposal. This paper presents experiment results on the use of fine and coarse aggregates from concrete waste in ...Reuse of concrete waste, especially in large quantity, can save not only material but also cost for its disposal. This paper presents experiment results on the use of fine and coarse aggregates from concrete waste in geopolymer mortars and concretes. Geopolymeric cement is an inorganic compounds of aluminosilicates synthesized from precursors with high content of silica and alumina activated by alkali silicate solutions. Geopolymer in this experiment was synthesized from fly ash as the precursor and sodium silicate solution as the activator. Hardening of geopolymers was performed by heating the casted paste in an oven at -60~Cfor 3 to 36 hours. Compressive strength of geopolymer pastes and mortars using either fresh or waste fine aggregates were in the range of 19-26 MPa. Hardening time of 3 hours at 60~C followed by leaving the test pieces at room temperature for 7 day before testing results in similar strength to that of mortars cured for 36 hours at 60~C followed by leaving the samples at room temperature for 3 days. It suggests that optimum strength can be achieved by combination of heating time and rest period before testing, i.e the specimens age. Applying mix design with a target strength of 40 MPa, conventional Portland cement concretes using fresh aggregates reached 70% of its target strength at day-7. Compressive strength of geopolymer concretes with waste aggregates was -25 MPa at day-3 while geopolymer concretes with fresh aggregates achieved -39 MPa at day-3. It can be concluded that geopolymer concretes can achieve the target strength in only 3 days. However, the expected reinforcing effect of coarse aggregates in concrete was ineffective if waste coarse aggregates were used as the strength of the concretes did not increase significantly from that of the mortars. On the other hand, waste fine aggregates can be reused for making geopolymer mortars having the same strength as the geopolymer mortars using fresh aggregates.展开更多
This article studies the effects of limestone powder on rheological properties of cement - fly ash mortar with RHEOLAB QC type rotation viscometer. The Bingham fluid model is introduced to fit the yielding stress and ...This article studies the effects of limestone powder on rheological properties of cement - fly ash mortar with RHEOLAB QC type rotation viscometer. The Bingham fluid model is introduced to fit the yielding stress and plastic viscosity of the mortar. The POWER LAW fluid model is introduced to fit the rheological index of the mortar. The results show that, adding limestone powder and fly ash to the cement mortar significantly decreases the yield stress of the mortar, changes the plastic viscosity of the mortar, increases the rheological index, decreases the degree of shear thinning of the mortar, and thereby improves the mortar＇ s workability. In the case of cement - fly ash mortar, with the increase of limestone powder content, both the yield stress and plastic viscosity of the mortar increase. When the limestone powder content is not higher than 14%, the increase of yield stress is not significant. When the limestone powder content is lower than 8%, the increase of plastic viscosity is not significant. When the content of limestone powder is higher than 22%, the rheological index of the mortar decreases and the degree of shear thinning increases. The effects of limestone powder＇ s packing density, shape and size, specific surface area, and fluid volume, are found to be the four major factors responsible for the changes ofrheological properties of the mortar.展开更多
文摘采用X-射线衍射(X-ray diffraction,XRD)、热重-差热扫描分析(TG-DSC)、扫描电子显微镜(scanning electron microscope,SEM)等方法对不同水化龄期掺4%速凝剂水泥净浆微观结构进行分析。结果表明:速凝剂的掺入显著影响水泥水化进程。在水泥-速凝剂-水体系中,Na Al O2及Na2CO3令石膏缓凝作用失效,铝酸三钙快速水化生成水化铝酸钙晶体,并与钙矾石及钠长石晶体形成相互攀附的网络结构对水泥颗粒产生"桥连"作用而实现速凝。同时,大量水化热促进水泥熟料矿物水化速率加快,净浆密实度快速增加。同时,随着水化龄期延长,净浆物相组成、钙矾石及氢氧化钙含量发生显著变化。
基金the National Nature Science Foundation of China （51272222）.
文摘Circulating fluidized bed combustion （CFBC） ash can be potentially used as supplementary cementitious materials for concrete production due to its desirable pozzolanic activity. The adsorption properties of CFBC ash-cement pastes were studied, and ordinary pulverized coal combustion （PCC） fly ash-cement pastes were used as control. The water-adsorption and superplasticizer （SP）-adsorption properties of the pastes were evaluated by water demand and UV-visible absorption spectroscopy respectively. The results show that CFBC ash-cement system has greater compressive strength as compared with PCC fly ash-cement system at a given curing age, although the water demand of the former is significantly higher than that of the latter. CFBC ash-cement pastes possess higher adsorption ability of aliphatic SP than PCC fly ash-cement pastes and the adsorption amount increases with an increase in ash replacement ratio. CFBC ash- cement pastes exhibit lower workability with higher slump loss. It is concluded that CFBC ash can be potentially used as supplementary cementitious material in concrete production, but the mix design of CFBC ash concrete needs to be appropriately adjusted. It is suggested that CFBC ash is used for the production of the concrete needing low flowability.
文摘Reuse of concrete waste, especially in large quantity, can save not only material but also cost for its disposal. This paper presents experiment results on the use of fine and coarse aggregates from concrete waste in geopolymer mortars and concretes. Geopolymeric cement is an inorganic compounds of aluminosilicates synthesized from precursors with high content of silica and alumina activated by alkali silicate solutions. Geopolymer in this experiment was synthesized from fly ash as the precursor and sodium silicate solution as the activator. Hardening of geopolymers was performed by heating the casted paste in an oven at -60~Cfor 3 to 36 hours. Compressive strength of geopolymer pastes and mortars using either fresh or waste fine aggregates were in the range of 19-26 MPa. Hardening time of 3 hours at 60~C followed by leaving the test pieces at room temperature for 7 day before testing results in similar strength to that of mortars cured for 36 hours at 60~C followed by leaving the samples at room temperature for 3 days. It suggests that optimum strength can be achieved by combination of heating time and rest period before testing, i.e the specimens age. Applying mix design with a target strength of 40 MPa, conventional Portland cement concretes using fresh aggregates reached 70% of its target strength at day-7. Compressive strength of geopolymer concretes with waste aggregates was -25 MPa at day-3 while geopolymer concretes with fresh aggregates achieved -39 MPa at day-3. It can be concluded that geopolymer concretes can achieve the target strength in only 3 days. However, the expected reinforcing effect of coarse aggregates in concrete was ineffective if waste coarse aggregates were used as the strength of the concretes did not increase significantly from that of the mortars. On the other hand, waste fine aggregates can be reused for making geopolymer mortars having the same strength as the geopolymer mortars using fresh aggregates.
文摘This article studies the effects of limestone powder on rheological properties of cement - fly ash mortar with RHEOLAB QC type rotation viscometer. The Bingham fluid model is introduced to fit the yielding stress and plastic viscosity of the mortar. The POWER LAW fluid model is introduced to fit the rheological index of the mortar. The results show that, adding limestone powder and fly ash to the cement mortar significantly decreases the yield stress of the mortar, changes the plastic viscosity of the mortar, increases the rheological index, decreases the degree of shear thinning of the mortar, and thereby improves the mortar＇ s workability. In the case of cement - fly ash mortar, with the increase of limestone powder content, both the yield stress and plastic viscosity of the mortar increase. When the limestone powder content is not higher than 14%, the increase of yield stress is not significant. When the limestone powder content is lower than 8%, the increase of plastic viscosity is not significant. When the content of limestone powder is higher than 22%, the rheological index of the mortar decreases and the degree of shear thinning increases. The effects of limestone powder＇ s packing density, shape and size, specific surface area, and fluid volume, are found to be the four major factors responsible for the changes ofrheological properties of the mortar.
