This study evaluates the pozzolanicity of Nyiragongo volcano lava flows in Congo by an indirect method using mortars with different rock powder proportions. The clinker used is a locally produced alite clinker, whose ...This study evaluates the pozzolanicity of Nyiragongo volcano lava flows in Congo by an indirect method using mortars with different rock powder proportions. The clinker used is a locally produced alite clinker, whose chemical and mineralogical composition was determined by XRF, Bogue and Taylor formulas. The lava flows were collected from the 2002, 2010 and 2021 eruption sites, and were characterized by XRF, CIPW normative mineralogy and geomechanical tests. The results show that Nyiragongo rocks are ultrabasic, silica- and alkali-rich, and contain minerals like nepheline, wollastonite and leucite. They satisfy the natural pozzolan criterion, and have pozzolanic activity indices above 70%. These rocks also have high RC and LA resistances, ranging from 190 MPa to 45 MPa, and from 18% to 32.6%, respectively. The rock powder addition in the mortars reduces mechanical resistances and increases setting times, except for a 5% replacement rate, which speeds up hardening. Nyiragongo lava can be used as a pozzolanic addition to produce a CEM II/B-P 32.5 cement.展开更多
The durability of the cement was mainly studied. Under 1.0 MPa of hydraulic pressure for 8 hours, water could penetrate completely through the sample made by portland cement, but could not penetrate through that by al...The durability of the cement was mainly studied. Under 1.0 MPa of hydraulic pressure for 8 hours, water could penetrate completely through the sample made by portland cement, but could not penetrate through that by alite-barium sulphoaluminate cement. Under the condition of freezing and thawing cycle, the loss ratio of compressive strength of the cement was only about 17.3% at curing 28 d ages, but the loss of portland cement was as high as 29.5%. Alite-calcium barium sulphoaluminate cement also has an excellent resistance to sulfate attack. The coefficients of resistance to sulfate attack of the cement exceeded 1.0. Meanwhile, the composition and microstructure of the hardened paste of alite-calcium barium sulphoaluminate cement were analyzed by XRD and SEM.展开更多
In this paper, uising the thermo-decomposition quantitative method to determine the alite content in cement clinker has been studied. It is shown that the alite content determined by the thermo-decomposition method is...In this paper, uising the thermo-decomposition quantitative method to determine the alite content in cement clinker has been studied. It is shown that the alite content determined by the thermo-decomposition method is very close to that obtained by the optical microscopy method. The practical quantitative analysis of alite in cement clinker was carried out by the thermo-decomposition method and a quite satisfactory result has been obtained.展开更多
The decomposition speed and mechanism of alite in Portland cement clinker are studied by means of optical microscopy, EPMA, XRD and chemical analysis. The results show that alite in portland cement clinker decomposes...The decomposition speed and mechanism of alite in Portland cement clinker are studied by means of optical microscopy, EPMA, XRD and chemical analysis. The results show that alite in portland cement clinker decomposes at the maximum speed when the temperature is at 1025 to approximately 1175 degree C. It takes about 40 hours for the alite in clinker burnt in the rotary kiln to completely decompose at 1175 degree C, and about 68 hours for the alite burnt in RSP-kiln. The presence of CaF//2 or CaSO//4 greatly affects the decomposition speed of alite. The former resists alite to decompose but the latter accelerates it and enables alite to decompose completely within 6 hours or less. (Author abstract) 3 Refs.展开更多
文摘This study evaluates the pozzolanicity of Nyiragongo volcano lava flows in Congo by an indirect method using mortars with different rock powder proportions. The clinker used is a locally produced alite clinker, whose chemical and mineralogical composition was determined by XRF, Bogue and Taylor formulas. The lava flows were collected from the 2002, 2010 and 2021 eruption sites, and were characterized by XRF, CIPW normative mineralogy and geomechanical tests. The results show that Nyiragongo rocks are ultrabasic, silica- and alkali-rich, and contain minerals like nepheline, wollastonite and leucite. They satisfy the natural pozzolan criterion, and have pozzolanic activity indices above 70%. These rocks also have high RC and LA resistances, ranging from 190 MPa to 45 MPa, and from 18% to 32.6%, respectively. The rock powder addition in the mortars reduces mechanical resistances and increases setting times, except for a 5% replacement rate, which speeds up hardening. Nyiragongo lava can be used as a pozzolanic addition to produce a CEM II/B-P 32.5 cement.
基金Funded by the National Natural Science Foundation of China (No.50672033)the "973"National Key Fundamental Research Plan ofChina (No.2009CB623101-1)
文摘The durability of the cement was mainly studied. Under 1.0 MPa of hydraulic pressure for 8 hours, water could penetrate completely through the sample made by portland cement, but could not penetrate through that by alite-barium sulphoaluminate cement. Under the condition of freezing and thawing cycle, the loss ratio of compressive strength of the cement was only about 17.3% at curing 28 d ages, but the loss of portland cement was as high as 29.5%. Alite-calcium barium sulphoaluminate cement also has an excellent resistance to sulfate attack. The coefficients of resistance to sulfate attack of the cement exceeded 1.0. Meanwhile, the composition and microstructure of the hardened paste of alite-calcium barium sulphoaluminate cement were analyzed by XRD and SEM.
文摘In this paper, uising the thermo-decomposition quantitative method to determine the alite content in cement clinker has been studied. It is shown that the alite content determined by the thermo-decomposition method is very close to that obtained by the optical microscopy method. The practical quantitative analysis of alite in cement clinker was carried out by the thermo-decomposition method and a quite satisfactory result has been obtained.
文摘The decomposition speed and mechanism of alite in Portland cement clinker are studied by means of optical microscopy, EPMA, XRD and chemical analysis. The results show that alite in portland cement clinker decomposes at the maximum speed when the temperature is at 1025 to approximately 1175 degree C. It takes about 40 hours for the alite in clinker burnt in the rotary kiln to completely decompose at 1175 degree C, and about 68 hours for the alite burnt in RSP-kiln. The presence of CaF//2 or CaSO//4 greatly affects the decomposition speed of alite. The former resists alite to decompose but the latter accelerates it and enables alite to decompose completely within 6 hours or less. (Author abstract) 3 Refs.
