Abstract

In recent years Venezuela has presented a crisis on the demand, commercialization and production of cement, the material needed for construction, therefor additive cements are being used without any type of regulations. This work presents the physical-mechanical characterization of three concrete mixtures with water / cement ratio of 0.45 and water / cement ratio of 0.60 with different types of Portland cement, Type I, Type CPCA1,and the third mixture corresponds to Type CPCA1 Rewarding it with a 15% addition in his own weight, developing a mixture of better quality. These concretes were characterized by: settling, setting time, percentage of total porosity, percentage of water absorption and mechanical resistance to compression. The results showed that the concrete mixture produced with CPCA1 does not meet the minimum requirements established in the Venezuelan standard for use in the elaboration of structural concrete, because among other parameters its resistance to compression it's below the design value. As for the CPCA1 giving it 15% addition in its own weight meets the requirements, and can be used in the manufacture of concrete structural elements.

Abstract

Abstract

The development of the cement industry consumes piles of natural resources and generating huge amount of waste and causing serious pollution, which can be partially solved by replacing with other cementitious materials, in particularly, solid waste. Reclaimed concrete slurry waste (RCSW), a corrosive and hazardous the residues from the reclaimed system for retrieving the aggregates from the returned concrete or cleaning the concrete mixer and trucks in the ready-mixed concrete plant, could that cannot be used to manufacture reclaimed concrete. However, the pre-hydration limits the hydraulic property of RCSW, which requires the proper treatment. This paper investigated the effect of three different treatment methods in improving the performance of RCSW and its feasibility of replacing cement under different substitution ratio in manufacturing reclaimed concrete. The treatment included sieving, shearing and ball-milling, and the substitution ratio was set as 15%, 30% and 45%, respectively. In addition to compressive strength and hydration properties, the environment impact of the cement paste replaced with RCSW were investigated as well. The results showed that compared within three methods, the shearing and ball-milling generated the treated RCSW with smaller particle size and high roundness. For the RCSW substituted cement paste, the substitution with 15% of treated RCSW provided the highest strength, meanwhile, while at a higher substitution ratio significantly reduced the compressive strength. The 15% of ball milling treated RCSW produced more products during the hydration process, resulting in a denser structure. According to the economic and environmental calculations, RCSW substitution reduced CO2 emissions, in which, the ball-milling method showed a lower carbon footprint.

Abstract

Blast furnace slag and lead-zinc tailings (LZTs) are solid wastes from the iron-making and mining industries, respectively. In order to reuse these solid wastes, the LZTs were pre-calcined at different temperatures and then explored whether it is capable of being the activator of slag. The effects of pre-calcination on the phase composition of LZTs were elucidated by XRD. The compressive strength of LZTs-activated slag pastes was investigated, and the mineral composition and microstructure of the pastes were detected by XRD and SEM. The results imply that with the elevating of heating temperature from 500 ℃ to 1000 ℃, the dolomite in LZTs decompose into CaO and MgO, and the oxidation of pyrite resulted in the formation of Fe2O3 and gaseous SO3, then SO3 reacted with a part of formed CaO to produce CaSO4. The resulting CaSO4 and CaO can become the sulfate activator and alkaline activator of slag, respectively. The LZTs-activated slag pastes prepared with the LZTs preheated at 800 ℃ exhibit the highest strength at 90 d, which yield 24 MPa. The hydration products of LZTs-activated slag were ettringite and calcium silicate hydrates (C-S-H gel). Large amounts of dense C-S-H gel bond together, connecting most of the ettringite networks into a whole, thus forming a dense structure and effectively improving the strength of LZTs-activated slag. The outcome of this study provides a potential disposing or reusing approach of the large amounts of LZTs.

Abstract

Experiments on the development of compressive strength and static and dynamic Young’s moduli were performed by the following mix proportions of concrete: the first uses different types of Portland cement without fly ash (FA) with a water-cement ratio of 45%, keeping at different curing temperatures; the second partially use FA in place of the cement, with the other conditions same as above; the third uses only blast furnace cement B instead of Portland cement. With these specimens, we comparatively examined in terms of temperature adjusted concrete age, how the mechanical properties change with the use of cement only, FA replacement for cement and with variation in curing temperatures. As a result, it was confirmed that the replacement of cement by fly ash enhanced the long-term mechanical properties of concrete regardless of the curing temperature applied in this experiment.

Abstract

Abstract

The local fired brick production technique is the known method of brick making, especially in Jimma Town. Firing of bricks in local brick production method is conducted by burning of much amount of woods. But this method of firing bricks by burning of woods will affect the environment. The locale firing technique is difficult to control the firing temperature, which will result in non-uniform burnt bricks. The major objective of this experimental study was to compare the compressive strengths of locally fired clay bricks and the local unfired cement and lime stabilized clay bricks. Specifically, the index properties of soil used for brick production, the compressive strength of locally fired clay bricks, and stabilized clay bricks had been determined and compare with the standard specifications. This study, it was used contents of the stabilizer for cement and lime of 10%, 12%, and 14%, respectively. The mix ratio applied 1:9, 1:7, and 1:6 by volume of clay with stabilizer 10%, 12%, and 14%. Based on the result on the 28th day, the mean compressive strength test, the 10%, 12%, and 14% cement Stabilized clay bricks have compressive strengths of 2.91Mpa, 3.28Mpa, and 3.79Mpa respectively, which are better than the mean compressive strength of the locally fired clay bricks which is 2.73Mpa. On the other hand, the 28th day means compressive strengths of the lime stabilized clay bricks were 2.19Mpa, 2.51Mpa, and 2.69Mpa, respectively. Therefore, these results showed that the Fired Clay Brick fails the minimum mean compressive strength requirement based on the ES, ASTM, and IS standards. But the Stabilized Clay Bricks fulfill the minimum compressive strength requirements of IS standard for stabilized bricks. Among these three methods, the cement stabilized clay bricks indicated better quality than both locally fired and lime stabilized bricks.

Abstract

Many years ago, consolidation accomplished by laborers wielding a variety of spades, tampers, and similar tools. In Ethiopia, there is no enough knowledge by the laborers, while the site engineers ignored the correct application due to some constraints. The agreement of acceptable vibration level in fresh concrete to which tamping time duration is optimum is an issue to obtain the desired specific compressive strength. This research study aims to evaluate the maximum time length and techniques used to Vibrating or Tamping fresh concrete and its effect on the compressive strength of C-25 Concrete through internal Rodding. Therefore, to study the effects of the period by vibrating or tamping, the needle-type internal vibrator was used to test new concrete cubes based on ACI309R-96. The quality of concrete is important to make physical tests on materials used before any actual experiments to perform. The fresh concrete samples tested by using internal vibration methods and techniques of compaction with different time duration of 1sec, 2sec, 3sec, 4sec, and 5sec. These tests performed by using steel rod in fresh concrete to know the Optimum time of compaction by internal vibration on the cube test of new concrete. Laboratory experiments had been conducted to check the methods and techniques applied to construction sites, as well as site observation on the effects of the vibration time of fresh concrete on the compressive strength and flexural strength of C-25 Concrete with varying vibration time duration and steel rod tamping. Based on the results of cube tests of compressive strength of Concrete Samples have been checked on the 3rd day, 7th day, and 28th day. This research study found out that the Optimum period of compaction was 3sec to produce an acceptable right quality of the concrete mix. Likewise, the flexural strength of the Concrete Sample, when it tested in the laboratory on the 7th day and 28th day, results revealed that the flexural strength improved when vibration time increased, but the amount of water has to be reduced to obtain the desired strength. Finally, Tamping is needed to place fresh concrete in the mold correctly. Furthermore, new concrete produced should match the properties and avoid improper tamping or vibration applications. This situation must not cause differences in the compressive strength of concrete.

Abstract

Many years ago, consolidation accomplished by laborers wielding a variety of spades, tampers, and similar tools. In Ethiopia, there is no enough knowledge by the laborers, while the site engineers ignored the correct application due to some constraints. The agreement of acceptable vibration level in fresh concrete to which tamping time duration is optimum is an issue to obtain the desired specific compressive strength. This research study aims to evaluate the maximum time length and techniques used to Vibrating or Tamping fresh concrete and its effect on the compressive strength of C-25 Concrete through internal Rodding. Therefore, to study the effects of the period by vibrating or tamping, the needle-type internal vibrator was used to test new concrete cubes based on ACI309R-96. The quality of concrete is important to make physical tests on materials used before any actual experiments to perform. The fresh concrete samples tested by using internal vibration methods and techniques of compaction with different time duration of 1sec, 2sec, 3sec, 4sec, and 5sec. These tests performed by using steel rod in fresh concrete to know the Optimum time of compaction by internal vibration on the cube test of new concrete. Laboratory experiments had been conducted to check the methods and techniques applied to construction sites, as well as site observation on the effects of the vibration time of fresh concrete on the compressive strength and flexural strength of C-25 Concrete with varying vibration time duration and steel rod tamping. Based on the results of cube tests of compressive strength of Concrete Samples have been checked on the 3rd day, 7th day, and 28th day. This research study found out that the Optimum period of compaction was 3sec to produce an acceptable right quality of the concrete mix. Likewise, the flexural strength of the Concrete Sample, when it tested in the laboratory on the 7th day and 28th day, results revealed that the flexural strength improved when vibration time increased, but the amount of water has to be reduced to obtain the desired strength. Finally, Tamping is needed to place fresh concrete in the mold correctly. Furthermore, new concrete produced should match the properties and avoid improper tamping or vibration applications. This situation must not cause differences in the compressive strength of concrete.

Abstract

Cement is one of the components of concrete plays a great role in the construction industry. Nevertheless, it is the most expensive and environmentally unfriendly material. Therefore, requirements for economical and more environmentally-friendly cementing materials have extended interest in other cementing materials that can be used as partial replacement of the ordinary Portland cement. This research was, conducted to examine the suitability of calcined termite hill clay powder as a cement replacing material in the production of C-25 grade concrete as a relief for this problem. The Termite Hill Clay sample was collected from Bokuluboma vicinity. The sample was calcined at the temperature of 650°C using muffle furnace, ground to the fineness of 150 µm and its chemical composition was investigated. Normal consistency and setting time of the paste having Ordinary Portland Cement and calcined termite hill clay powder from 0% to 40% replacement in 5% increment percentage investigated. The compressive strength of eight different concrete mixes with the CTHCP replacing the ordinary Portland cement prepared for 22MPa and 34MPa (i.e., for 7th and 28th days targeted compressive strength) concrete with water cement ratio of 0.5 and 360kg/m3 cement content. The properties of the mixture assessed both at the fresh and hardened state. Results revealed that calcined termite hill clay powder found pozzolanic and can partially replace cement. It has shown that up to 11.3% replacement of the ordinary Portland cement by CTHCP, the cubes achieved a target mean compressive strength of C-25 grade concrete at 28th day 34Mpa. Although, the replacement percentage greater than 11.3% of the cement of calcined termite hill clay powder in the concrete has shown a slightly lower compressive strength. Moreover, the mix indicated workable up to 25% replacement percentage and also the setting time of the paste containing calcined termite hill clay powder found faster than that of the control mix. Hence, it is concluded that CTHCP was suitable to replace cement partially with 11.3% replacement of cement by calcined termite hill clay powder as the optimal percentage of the production of C-25 grade concrete. The fresh concrete mix was workable up to 25% replacement, and the mineral admixture served as an accelerator which is suitable for cold weather concreting works.