To study the deterioration mechanisms of anhydrite rock under the freeze-thaw weathering process,the physico-mechanical characteristics and microstructure evolutions of anhydrite samples were determined by a series of...To study the deterioration mechanisms of anhydrite rock under the freeze-thaw weathering process,the physico-mechanical characteristics and microstructure evolutions of anhydrite samples were determined by a series of laboratory tests.Then,a descriptive-behavioral model was used to measure the integrity loss in anhydrite samples caused by cyclic freeze-thaw.Finally,the freeze-thaw damage mechanisms of anhydrite rock were revealed from the macro and micro aspects.The results show that the pore size of the anhydrite rock is mainly concentrated in the range of 0.001-10μm.As the number of freeze-thaw cycles increases,there is a growth in the proportion of macropores and mesopores.However,the proportion of micropores shows a declining trend.The relations of the uniaxial compressive strength,triaxial compressive strength,cohesion,and elastic modulus versus freeze-thaw cycles can be fitted by a decreasing exponential function,while the internal friction angle is basically unchanged with freezethaw cycles.With the increase of confining pressure,the disintegration rates of the compressive strength and the elastic modulus decrease,and the corresponding half-life values increase,which reveals that the increase of confining pressures could inhibit freeze-thaw damage to rocks.Moreover,it has been proven that the water chemical softening mechanism plays an essential role in the freeze-thaw damage to anhydrite rock.Furtherly,it is concluded that the freeze-thaw weathering process significantly influences the macroscopic and microscopic damages of anhydrite rock.展开更多
The objective of this work is to improve the physical and mechanical properties of stabilized earth blocks (BTC) used in construction in the Ndé department of Cameroon. To achieve this, two stabilizers, cement an...The objective of this work is to improve the physical and mechanical properties of stabilized earth blocks (BTC) used in construction in the Ndé department of Cameroon. To achieve this, two stabilizers, cement and sawdust, were used at varying percentages of 0%, 4%, 6%, and 8%. Physical characterization tests, including natural water content, specific weight, jar test, Protor, and Atterberg limits, were conducted. Additionally, mechanical tests, such as compression and three-point bending, were performed. The results show that as the amount of stabilizer increases, the density of BTC decreases. The samples with 8% sawdust have the highest density, while those without stabilizers have the lowest. Porosity decreases as sawdust and cement content increases, with smaller values observed in samples with 8% sawdust or cement. Our tests indicate that blocks stabilized with cement have slightly higher compressive strength than those stabilized with sawdust. However, the water absorption rate increases with higher sawdust content.展开更多
Cemented backfill used in deep mines would inevitably be exposed to the ambient temperature of 20−60℃in the next few decades.In this paper,two types of cemented gravel sand backfills,cemented rod-mill sand backfill(C...Cemented backfill used in deep mines would inevitably be exposed to the ambient temperature of 20−60℃in the next few decades.In this paper,two types of cemented gravel sand backfills,cemented rod-mill sand backfill(CRB)and cemented gobi sand backfill(CGB),were prepared and cured at various temperatures(20,40,60℃)and ages(3,7,28 d),and the effects of temperature and age on the physico-mechanical properties of CRB and CGB were investigated based on laboratory tests.Results show that:1)the effects of temperature and age on the physico-mechanical properties of backfills mainly depend on the amount of hydration products and the refinement of cementation structures.The temperature has a more significant effect on thermal expansibility and ultrasonic performance at early ages.2)The facilitating effect of temperature and age on the compressive strength of CGB is higher than that on CRB.With the increase of temperature,the compressive failure modes changed from X-conjugate shear failure to tensile failure,and the integrity of specimens was significantly improved.3)Similarly,the shear performance of CGB is generally better than that of CRB.The temperature has a weaker effect on shear strength than age,but the shear deformation and shear plane morphology are closely related to temperature.展开更多
The aim of this work is to improve the high performance of mud bricks. The latter was reinforced with rice straws as stabiliser leading to an improvement of the physico-mechanical properties. Thus, the physical charac...The aim of this work is to improve the high performance of mud bricks. The latter was reinforced with rice straws as stabiliser leading to an improvement of the physico-mechanical properties. Thus, the physical characteristics of the clay such as natural water content, density, atterberg limit, plasticity limit (Wp) and plasticity index (Ip) were determined. Their values are respectively 8.39%, 2025.73 Kg/m<sup>3</sup>, 47.66%, 29.75% and 17.91%. The clay used is a low plastic organic silt. The normal proctocol provided an optimum dry density (ɣOP) of 1.28 Kg/m<sup>3</sup> at an optimum moisture content of 12.42%. The actual density of the straw is 464 Kg/m<sup>3</sup>, its absorption rate reached 206% in 5 mins and stabilised at 385% at 480 mins of immersion. The maximum bending and compression strengths are respectively 1.52 and 0.164 MPa. The mud brick absorption coefficients obtained are between 4.875 at 0% straw and 20.573% at 3% straw.展开更多
The present work consisted in carrying out a study on the effective formulation of concrete for an optimal resistance to compression (fc28) between 20 and 30 MPa for the sites animated by the actors of the informal an...The present work consisted in carrying out a study on the effective formulation of concrete for an optimal resistance to compression (fc28) between 20 and 30 MPa for the sites animated by the actors of the informal and semi-informal sectors of the construction. Studies have been carried out on projects under construction, by taking samples of fresh concrete in order to evaluate their real compressive strengths. These surveys show that there is a problem in the concrete formulation, as nearly 2/3 of the results show the lack of technical knowledge on concrete formulation practices. Indeed, on eight sites surveyed and whose fresh concrete samples were taken, only two sites (7 and 8) report fairly consistent results. Their 28-day compressive strength values are respectively 35.36 and 22.18 MPa. In addition, various formulations proposed with aggregates from different quarries or extracts from the bed of the Congo River, were determined in the laboratory. This study allowed us to obtain fairly objective results overall, which is characteristic of concretes of required quality. Of the six (06) formulation proposals, average resistances of 19.6 MPa at 07 days and 25.28 MPa at 28 days were obtained. These results at 28 days are in the range of 20 to 30 MPa, set as objective in this study. These formulations can be a reliable source for concrete manufacturers in these construction sectors. Similarly, the statistical study based on principal component factor analysis tests has shown that the most appropriate formulation, in terms of mechanical resistance, is that proposed with sand extracted from the Congo River (formulation 3). This is justified by the fact that this sand is consistent and has a good granular distribution.展开更多
The main objective of this study is to contribute to the optimization of the formulation of sand concretes and its valorisation according to natural sands from different quarries or extraction sites. Physical characte...The main objective of this study is to contribute to the optimization of the formulation of sand concretes and its valorisation according to natural sands from different quarries or extraction sites. Physical characteristics of natural sands have been determined and improved by the addition of crushing sand, taking into account the too fine elements of the sand. Four types of sand were used (Congo River, Djiri, Mfilou, crushed sand). The concrete formulations proposed from improved sands (30% crushed sand and 70% natural sand) reveal an increase in mechanical strength. Thus, it appeared that this improvement of the natural fine sands by the crushing sand has brought a clear increase in the maneuverability of the concretes and the physico-mechanical characteristics of nearly 50%, although this crushing sand has a sand equivalent value of less than 70%. These results augur well for the durability of structures in the construction industry in Congo.展开更多
This paper presents the findings on thermal expansion behavior of slaked lime doped rice husk silica(RHS)refractory monitored between 25℃and 1500℃.It also reports the phase transition analysis within the temperature...This paper presents the findings on thermal expansion behavior of slaked lime doped rice husk silica(RHS)refractory monitored between 25℃and 1500℃.It also reports the phase transition analysis within the temperature range of 850-1450℃.A sudden expansion of 0.7%noticed at 220℃is due to the transformation ofα-cristobalite toβ-cristobalite.The highest expansion(0.85%)reached within the temperature range of 650-850℃,remains almost constant for the investigated temperature range,and is not high enough to cause macro cracks in the refractory.The phase transition order is similar to those reported for quartzite refractory after 600℃,though the crystallization temperature is lowered due to the presence of the dopant.Modulus of rupture,apparent porosity,bulk density,refractoriness and reheat change are reported and their results meet with the standards qualifying them for use in coke ovens.展开更多
基金the National Natural Science Foundation of China for financial support (Grant No. 51578091)
文摘To study the deterioration mechanisms of anhydrite rock under the freeze-thaw weathering process,the physico-mechanical characteristics and microstructure evolutions of anhydrite samples were determined by a series of laboratory tests.Then,a descriptive-behavioral model was used to measure the integrity loss in anhydrite samples caused by cyclic freeze-thaw.Finally,the freeze-thaw damage mechanisms of anhydrite rock were revealed from the macro and micro aspects.The results show that the pore size of the anhydrite rock is mainly concentrated in the range of 0.001-10μm.As the number of freeze-thaw cycles increases,there is a growth in the proportion of macropores and mesopores.However,the proportion of micropores shows a declining trend.The relations of the uniaxial compressive strength,triaxial compressive strength,cohesion,and elastic modulus versus freeze-thaw cycles can be fitted by a decreasing exponential function,while the internal friction angle is basically unchanged with freezethaw cycles.With the increase of confining pressure,the disintegration rates of the compressive strength and the elastic modulus decrease,and the corresponding half-life values increase,which reveals that the increase of confining pressures could inhibit freeze-thaw damage to rocks.Moreover,it has been proven that the water chemical softening mechanism plays an essential role in the freeze-thaw damage to anhydrite rock.Furtherly,it is concluded that the freeze-thaw weathering process significantly influences the macroscopic and microscopic damages of anhydrite rock.
文摘The objective of this work is to improve the physical and mechanical properties of stabilized earth blocks (BTC) used in construction in the Ndé department of Cameroon. To achieve this, two stabilizers, cement and sawdust, were used at varying percentages of 0%, 4%, 6%, and 8%. Physical characterization tests, including natural water content, specific weight, jar test, Protor, and Atterberg limits, were conducted. Additionally, mechanical tests, such as compression and three-point bending, were performed. The results show that as the amount of stabilizer increases, the density of BTC decreases. The samples with 8% sawdust have the highest density, while those without stabilizers have the lowest. Porosity decreases as sawdust and cement content increases, with smaller values observed in samples with 8% sawdust or cement. Our tests indicate that blocks stabilized with cement have slightly higher compressive strength than those stabilized with sawdust. However, the water absorption rate increases with higher sawdust content.
基金Project(P2018G045)supported by the Science&Technology Research and Development Program of China RailwayProject(2018CFA013)supported by the Hubei Provincial Natural Science Foundation Innovation Group,China+1 种基金Project(KFJ-STS-QYZD-174)supported by the Science and Technology Service Network Initiative of the Chinese Academy of SciencesProject(51709257)supported by the National Natural Science Foundation of China。
文摘Cemented backfill used in deep mines would inevitably be exposed to the ambient temperature of 20−60℃in the next few decades.In this paper,two types of cemented gravel sand backfills,cemented rod-mill sand backfill(CRB)and cemented gobi sand backfill(CGB),were prepared and cured at various temperatures(20,40,60℃)and ages(3,7,28 d),and the effects of temperature and age on the physico-mechanical properties of CRB and CGB were investigated based on laboratory tests.Results show that:1)the effects of temperature and age on the physico-mechanical properties of backfills mainly depend on the amount of hydration products and the refinement of cementation structures.The temperature has a more significant effect on thermal expansibility and ultrasonic performance at early ages.2)The facilitating effect of temperature and age on the compressive strength of CGB is higher than that on CRB.With the increase of temperature,the compressive failure modes changed from X-conjugate shear failure to tensile failure,and the integrity of specimens was significantly improved.3)Similarly,the shear performance of CGB is generally better than that of CRB.The temperature has a weaker effect on shear strength than age,but the shear deformation and shear plane morphology are closely related to temperature.
文摘The aim of this work is to improve the high performance of mud bricks. The latter was reinforced with rice straws as stabiliser leading to an improvement of the physico-mechanical properties. Thus, the physical characteristics of the clay such as natural water content, density, atterberg limit, plasticity limit (Wp) and plasticity index (Ip) were determined. Their values are respectively 8.39%, 2025.73 Kg/m<sup>3</sup>, 47.66%, 29.75% and 17.91%. The clay used is a low plastic organic silt. The normal proctocol provided an optimum dry density (ɣOP) of 1.28 Kg/m<sup>3</sup> at an optimum moisture content of 12.42%. The actual density of the straw is 464 Kg/m<sup>3</sup>, its absorption rate reached 206% in 5 mins and stabilised at 385% at 480 mins of immersion. The maximum bending and compression strengths are respectively 1.52 and 0.164 MPa. The mud brick absorption coefficients obtained are between 4.875 at 0% straw and 20.573% at 3% straw.
文摘The present work consisted in carrying out a study on the effective formulation of concrete for an optimal resistance to compression (fc28) between 20 and 30 MPa for the sites animated by the actors of the informal and semi-informal sectors of the construction. Studies have been carried out on projects under construction, by taking samples of fresh concrete in order to evaluate their real compressive strengths. These surveys show that there is a problem in the concrete formulation, as nearly 2/3 of the results show the lack of technical knowledge on concrete formulation practices. Indeed, on eight sites surveyed and whose fresh concrete samples were taken, only two sites (7 and 8) report fairly consistent results. Their 28-day compressive strength values are respectively 35.36 and 22.18 MPa. In addition, various formulations proposed with aggregates from different quarries or extracts from the bed of the Congo River, were determined in the laboratory. This study allowed us to obtain fairly objective results overall, which is characteristic of concretes of required quality. Of the six (06) formulation proposals, average resistances of 19.6 MPa at 07 days and 25.28 MPa at 28 days were obtained. These results at 28 days are in the range of 20 to 30 MPa, set as objective in this study. These formulations can be a reliable source for concrete manufacturers in these construction sectors. Similarly, the statistical study based on principal component factor analysis tests has shown that the most appropriate formulation, in terms of mechanical resistance, is that proposed with sand extracted from the Congo River (formulation 3). This is justified by the fact that this sand is consistent and has a good granular distribution.
文摘The main objective of this study is to contribute to the optimization of the formulation of sand concretes and its valorisation according to natural sands from different quarries or extraction sites. Physical characteristics of natural sands have been determined and improved by the addition of crushing sand, taking into account the too fine elements of the sand. Four types of sand were used (Congo River, Djiri, Mfilou, crushed sand). The concrete formulations proposed from improved sands (30% crushed sand and 70% natural sand) reveal an increase in mechanical strength. Thus, it appeared that this improvement of the natural fine sands by the crushing sand has brought a clear increase in the maneuverability of the concretes and the physico-mechanical characteristics of nearly 50%, although this crushing sand has a sand equivalent value of less than 70%. These results augur well for the durability of structures in the construction industry in Congo.
基金This work was supported in part by the Malaysian Ministry of Science,Technology&Innovation(MOSTI)E-Science Fund(Project Code 03-02-02-SF0089)and UTP graduate assistantship scheme.
文摘This paper presents the findings on thermal expansion behavior of slaked lime doped rice husk silica(RHS)refractory monitored between 25℃and 1500℃.It also reports the phase transition analysis within the temperature range of 850-1450℃.A sudden expansion of 0.7%noticed at 220℃is due to the transformation ofα-cristobalite toβ-cristobalite.The highest expansion(0.85%)reached within the temperature range of 650-850℃,remains almost constant for the investigated temperature range,and is not high enough to cause macro cracks in the refractory.The phase transition order is similar to those reported for quartzite refractory after 600℃,though the crystallization temperature is lowered due to the presence of the dopant.Modulus of rupture,apparent porosity,bulk density,refractoriness and reheat change are reported and their results meet with the standards qualifying them for use in coke ovens.
