| Portland cement has been commonly used worldwide as the most popular cementitious binder in preparation of many cement based materials.When Portland cement is added together with water and fine aggregates,the resulted mixture is called cement mortar.The fine aggregate can be of a variety types but the most commonly used is river sand.Also,crushed rock fines or manufactured,artificial,engineered sand can be used as fine aggregate.Nevertheless,as though the construction materials production has depended on natural resources for many decades,the severe environmental and economical concerns due to the extensive Portland cement manufacturing and shortage in natural resources emerged.The cement production generally produces enormous amount of carbon dioxide（CO2）which is directly emitted into the atmosphere.Abundance of CO2 in atmosphere has diverse consequences on the globe ecosystem.Another factor contributing to the degradation of the environment is inadequate exploitation of natural resources for production of mineral aggregates which has become the principal cause of erosion in some regions.Nowadays,a trend development in construction is oriented to modernization of conventional methods and promotion of sustainable and friendly environmental construction materials.Many new building materials have already been introduced into construction practice and others are still being evaluated.The evolution in civil engineering materials is triggered by the need of providing basic necessary infrastructures to the world’s habitants and some governmental restrictions for the sake of protection of environment and ecological balance.The modern cementitious composites differ from the traditional because of the advance in technology.In addition,a number of measures and strategies such as the reuse of construction demolition waste（bricks,concrete）,reducing consumption of cement by adding more mineral admixtures into the mix proportions,replacing natural sand by artificial sand have been established.The method of partially or fully substitute cement or aggregates is becoming popular among construction practitioners.This approach provides possibilities for improving the quality of cement mortar and concrete in efficient way.However,each amount of supplementary cementitious material added to the mixture can change the structure and properties of the mortar or concrete.Wherefore,it is a necessity to respect the construction materials standards.In this study we used the method of partially and fully replacing mix proportion constituents with purpose to evaluate physical and mechanical properties of the cement mortar.The raw materials basalt rock powder,superfine sand,standard sand,and artificial sand were collected from local resources of Lanzhou,Gansu Province.The binder used was Qilian Mountains brand Portland cement with strength grade 42.5 which was supplied by Gansu Cement Factory Ltd.In addition,the mixing water was saturated water from local supplier.Besides,the laboratory equipments included an electronic balance with precision of 0.01g,KIC electric cement mixer,NT 2000 cement mortar vibration compressor,YES-2000 compression testing machine,NM-4A non-metallic ultrasonic testing and analysis apparatus,and STDT-12concrete dynamic elastic modulus tester.In order to study the influence of the blending of basalt rock powder and superfine sand on the performance of cement mortar,different mixing ratios were designed for testing.Firstly,the superfine sand was used to replace the artificial sand to prepare the mortar test blocks;the substitution ratios were 10%,20%,30%,40%and 50%,respectively.The effect of replacing artificial sand with superfine sand on cement mortar performance was investigated.Afterwards,attempt of using basalt rock powder instead of Portland cement was made,with replacement ratios varying from 10%,15%,20%,25%,30%,respectively.Finally,a group of cement mortar mixtures with good performance was selected from the obtained experimental results.Amongst designed mortar mixtures ratios,the best ratio of basalt rock powder as partial replacement of Portland cement was 10%and 15%and for the superfine sand as partial substitution of artificial sand was 10%and 20%.According to"Cement mortar strength test method（ISO method）"GB/T17671-1999,40 mm×40 mm×160 mm prism cement mortar test blocks were prepared.The experimental procedure proceeded with accurately weight the amount of material required to prepare the test block according to the designed mixing ratio,and then use the universal cement mixer to stir the materials used.During mixing,water was added cautiously,first the water is put into the stirring pot,after the Portland cement was added,start stirring,then stir at low speed for30s,and at the same time start the second 30s,and evenly the fine aggregate was added.Immediately after the mixture was obtained,it was molded on a vibrating table,and the mortar was placed in two layers into the test mold during vibration molding.The test samples were cured in moisture for 24 hours and under the specified curing conditions after demolding.After the samples reached the required testing age,tests were carried out.At first,the strength test of the mortar by using non-destructive testing methods was performed,such as measuring the mass,ultrasonic pulse velocity and dynamic elastic modulus,besides the measurement resumed after 120 days.In the strength test also the flexural strength test was carried out,and after each fracture,the compressive strength test proceeded.During the entire loading process,the pressure receiving surface was the two sides of the test sample,and the area is 40 mm×40 mm.The range of 2400 N/s±200 N/s is evenly loaded until destruction.The ages for determining the flexural strength and compressive strength were 3,7,14,21,28,56,90 and 120 days,respectively.The influence of basalt rock powder and superfine sand proportions and age variation on the performance of cement mortar was studied.Moreover,the drying shrinkage test of mortar was carried out in accordance to JC/T603-2004"Test method for dry shrinkage of cement mortar".The formulated cement mortar samples were in form of a prism with dimensions of 25 mm×25 mm×280 mm,also the end plate had a hole for measuring the nail head.The position should be such that the measuring head of the test piece after molding is on the axis of the test sample,and the depth of the test head when the test sample is formed should be 10 mm±1 mm.The molded test samples were demolded after curing for 24 hours under standard curing conditions;after demolding the samples were placed in water for two days,after which the cement mortar samples were removed from the water to clean the surface and the dirt of the nail head;after,cement mortar samples were tested.Thanks to length gauge the quality of cement mortar was assessed by measuring the dry shrinkage deformation;the evaluation lasted 28 days and the impact basalt rock powder and superfine sand on the drying shrinkage performance of cement mortar was studied.The test results showed that when basalt rock powder was used instead of Portland cement to prepare the mortar,the flexural strength and compressive strength of the mortar decreased with the increase of Portland cement replacement proportions under the same age.When the ratio of basalt rock powder to Portland cement was 10%at the age of 3 days,flexural strength of the mortar decreased by 2.6%compared with the reference mortar;at the age of 28 days,flexural strength diminished by 8.6%.With the increase of the replacement ratio of basalt rock powder,the flexural strength of the mortar continued to decrease.When the replacement ratio was 30%,at the age of 3 days,flexural strength of the mortar decreased by 32.9%;but,by the age of 28days flexural strength had decreased by 19.3%.For the compressive strength,the change trend was similar to the flexural strength.When the basalt rock powder replacement ratio was 10%,at the age of 3 days,compressive strength was 4.4%lower than the reference mortar;however,by the age of 28 days,compressive strength had decreased by 14.3%.When the basalt rock powder replacement content was increased to 30%at the age of 3 days,compressive strength decreased by 26.5%;in addition,by at the age of 28 days,compressive strength had decreased by 35.9%.However,when the age reached 90 days,the change gap diminished;for instance,when the basalt powder replacement quantity was reduced to 10%,the difference was only 1.3%but,when the basalt rock powder replacement amount was increased to 30%,the change gap also increased to 18.8%.The quality of the cement mortar increased with the increase of the replacement ratio of basalt rock powder.Therefore,at the age of 3 days,the weight of cement mortar that contains basalt rock powder ranging from 10%,15%,20%,25%,30%,increased by 0.05%,1.42%,8.91%,1.68%,and 6.09%respectively.When cement mortar aged 7 days,while the replacement ratio of Portland cement with basalt rock powder increased on contrary,the dynamic elastic modulus and ultrasonic velocity of the mortar decrease.When the amount of basalt rock powder was 10%,15%,20%,25%and30%the dynamic elastic modulus of mortar decreased by 14.8%,25.3%,18.1%,21.1%and20.3%respectively,compared with the reference mortar.Therefore,the longitudinal ultrasonic pulse velocity of the cement mortar reduced by 1.1%,4.0%,0.3%,3.1%,and 4.3%,respectively;the transverse ultrasonic pulse velocity of the cement mortar diminished by 2.5%,6.3%,5.1%,11.7%and 8.2%,respectively,compared with the reference mortar.When the mortar was prepared by partial replacing artificial sand with superfine sand,the flexural strength and compressive strength of the mortar decreased with the increase of the superfine sand replacement proportion under the same age of the mortar.When the ratio of artificial sand replacement with superfine sand was 10%,at the age of 3 days,flexural strength decreased by 0.2%compared with the reference mortar;but,by the age of 28 days,flexural strength had decreased by 2.8%.With the increase of the superfine sand substitution amount,the flexural strength of the mortar continued to decrease.When the replacement ratio was 50%,at the age of 3 days,flexural strength of the mortar decreased by 21.6%;however,by the age of 28 days,flexural strength decreased by 28.1%.For compressive strength,when artificial sand substitution proportion with superfine sand was 10%,at the age of 3 days,compressive strength was 0.7%which was lower than the reference mortar;but,by the age of 28 days,compressive strength had decreased by8.0%.When the superfine sand quantity increased to 50%,at the age of 3 days,compressive strength decreased by 12.1%;however,by the age of 28 days,compressive strength had decreased by 31.8%.Besides,when the age reached 56 days,and the artificial sand substitution with superfine sand was 10%,the compressive strength of the mortar increased by 2.8%compared with the reference mortar and also,the compressive strength increased by 0.9%at the age of 90 days.The analysis shows that small amount of superfine sand has a partial increase in the late strength of the mortar.The quality of the cement mortar increased with the increase of the ratio of artificial sand replacement with superfine sand.Therefore,at the age of 28 days,when the artificial sand replacement ratio with superfine sand ranged from 10%,20%,30%,40%,50%,The quality of cement mortar increased by 3.97%,2.87%,3.31%,3.98%,and 0.52%respectively,compared with the reference mortar.At the same age of the cement mortar,the dynamic elastic modulus and the ultrasonic pulse velocity of the cement mortar decreased as artificial sand replacement quantity with superfine sand increases.At the age of 28 days,the cement mortar that contains superfine sand ranging from 10%,20%,30%,40%,50%,the dynamic elastic modulus of mortar was 4.7%,2.8%,6.8%,9.4%and13.5%which was comparably lower than that of reference mortar.The longitudinal ultrasonic pulse velocity of the mortar reduced by 5.4%,0.8%,4.9%,3.8%and 6.2%,respectively and also,the transverse ultrasonic pulse velocity of the mortar reduced by 1.3%,0.7%,2.5%,1.2%and1.3%respectively,compared with the reference mortar.Despite the reduction of physical and mechanical properties of cement mortar,basalt rock powder and superfine sand could be used as replacement of Portland cement and artificial sand,indeed,in account of ratio between 10%and25%basalt rock powder by Portland cement weight and 10%to 20%superfine sand by volume of artificial sand.These replacement proportions showed comparable results as those of the reference cement mortar.Therefore,under appropriate circumstances,basalt rock powder and superfine sand can be used in cement mortar to replace some raw materials to achieve environmental protection and natural resources conservation.This approach also complies with the concept of sustainable development and further research about basalt rock powder and superfine sand application is recommended. |
PDF Full Text Request