Experimental Investigation on Grades of Cement in the Nominal and Design Concrete Mixes

In India, the experience in the use of concrete in housing is more than seven decades old. Concrete mix is a combination of cement, water and aggregates of sand and stone. The relative merits of using 33, 43 & 53 grades of cement in the nominal and design concrete mixes are studied, by testing to destruction hundreds of cubes, cylinders and prisms made using these three grades of cement, the concrete mix having been designed as per the relevant Indian Standard code of practice. The objective of this paper is to make awareness among researchers, engineers and the public about the latest scientific and technical developments in cement, and how to achieve economy in concrete. The foremost objective of concrete mix design is to hand-pick the optimum proportions of various ingredients of the concrete to satisfy the required properties in its fresh and hardened state. As per the investigation, if concrete mixes are designed for different grades adopting separately 33, 43, & 53 grades of cements, grade 53 gives the highest 28 days cube strength, whereas 33 grade cement gives the lowest value. The relative cost of using these three grades is also discussed in the paper.

Cement Equivalence of Metakaolin for Workability, Cohesiveness, Strength and Sorptivity of Concrete

A series of concrete mixes with metakaolin (MK) content ranging from 0 to 30% and water/cementitious materials (W/CM) ratio varying from 0.30 to 0.50 were produced for performance testing. The results showed that adding MK up to 20% as ordinary Portland cement (OPC) replacement best improved the 28-day and 70-day cube strengths, whereas adding MK up to 30% as OPC replacement always increased the cohesiveness and decreased the sorptivity, but impaired the workability. Moreover, the cement equivalent factor (CEF), i.e. the equivalent mass of OPC per mass of MK added, for each performance attribute, including workability and cohesiveness, was evaluated. Whilst the actual CEF of MK was generally higher at a higher W/CM ratio and lower at a higher MK content, overall, the average CEFs were found to be 1.98, 2.17, 3.83, 1.93, 2.12, and 4.70 for slump, flow, cohesiveness, 28-day cube strength, 70-day cube strength, and sorptivity coefficient, respectively. These CEF values indicated that the MK is a highly effective cementitious material for improving the cohesiveness, strength, and durability. Moreover, it has been demonstrated that the CEFs for workability and cohesiveness are useful parameters in aiding the mix design of MK concrete.

The Properties of Concrete Based on Steel Slag as a By-Product of Metallurgical Production

This article presents the results of research on the use of unstable steel slag with a fraction of 0/8 mm as a 100% substitute for natural aggregate in concrete production. Two types of cements were used for the production of concrete: Portland cement CEM I 42.5N and hybrid cement H-CEMENT. Both of these cements were produced by the company Považská cementárna, a.s., Ladce. The main objective of this study was to assess the suitable type of binder to be combined with unstable steel slag in the production of concrete composite. The prepared concrete was used to test the properties of a fresh concrete mix, i.e. its consistency and bulk density. Hardened concrete was used to test the strength and deformation properties, including cube strength after 3, 7, 14, 21, 28 and 90 days, as well as prism strength after 28 days. The static modulus of elasticity was determined using prisms after 28 days of age of the test specimens. Our attention was also focused on determining the class of leachability of the concretes based on steel slag with CEM I 42.5N and H-CEMENT. The durability of concrete prepared on the basis of steel slag was tested in an environment with increased temperature and pressure. The results of the strength characteristics tests show a difference between the 28-day average cube strength of concrete using CEM I 42.5N and H-CEMENT (34.6 MPa and 29.1 MPa), while after 90 days, the average cube strength value stabilized at about 38 MPa. The average values ​​of the static modulus of elasticity when using CEM I 42.5N and H-CEMENT are almost identical, achieving values ​​of 32.5 GPa and 32.8 GPa, respectively. Concrete based on steel slag with CEM I 42.5N and H-CEMENT can be included in leachability class IIb. The results of the durability test of concrete based on steel slag in an environment with increased temperature and pressure confirmed the use of H-CEMENT hybrid cement from the company Považská cementáren, a.s., Ladce, as a suitable binder. .

Mechanical and Fatigue Parameters of Two Types of Alkali-Activated Concrete

The alkali-activated concrete is prepared as a new potential material for the production of concrete elements developed by ZPSV, a. s. company. Note that civil engineering structures are usually made of ordinary Portland cement (OPC) based concrete but today, the cement industry is responsible for emitting between 6% and 7% of all the CO2 emission into the atmosphere. Therefore, it is essential to seek different binders to provide environmental friendly materials. One possible alternative is the application of alkali-activated concrete. The optimal design of concrete mixture was studied in this investigation. Two types of concrete have a similar application and therefore the fatigue parameters can be compared. To this aim, specimens were prepared and tested under static (compressive cube strength) and cyclic loading (fatigue parameters − Wöhler curve). The experimentally obtained results (both mechanical and fatigue) of both types of concrete are compared and the suitability of these types of composites for its application is discussed.

Mechanical Properties and Permeability of Previous Color Recycled Aggregate Concrete

Experimental study was carried out on compressive cube strength, flexural strength and permeability coefficient of color permeable concrete using concrete waste as coarse recycled aggregate. The results show that watercement ratio has significant effect on compressive cube strength, flexural strength and permeability coefficient of color permeable recycled aggregate concrete (RAC).The flexural strength of RAC is improved by polypropylene fiber. The content of pigment from 5% to 10% has no impact on mechanical properties and permeability of RAC.

Effect Of Specimen Size and Shape on Compressive Strength of Self-Compacting Concrete

This study aims to show the effect of specimen size and shape on compressive strength of self-compacting concrete (SCC). The work is divided into two parts, the first was to designed Normal Concrete (NC), High Strength Concrete (HSC) and Self Compacting Concrete (SCC) of strength between (25-70) MPa. from locally available materials. The values percent of cylinder to cube strength were between (0.86-0.9), (0.94-0.96), (0.96-0.99) of NC, HSC and SCC respectively.The second is to investigate the effect of specimen size on compressive strength, the values of correction factor of cube specimens (150*150*150)mm and (100*100*100)mm is (0.89-1.29), (0.98-1.26) and (0.98-1.22) of NC,HSC and SCC respectively. The values of correction factor of cylinder specimens of (150*300) mm and (100*200) mm is (0.88-1.08), (0.93-1.07) and (0.95-1.04) of NC, HSC and SCC respectively.

Determination of Concrete Cube Strength from Used Samples / Určení Krychelné Pevnosti Betonu U Použitých Zkušebních Trámců

This paper deals with the determination of compressive strength of concrete. Cubes, cylinders and re-used test beams were tested. The concrete beams were first subjected to three-point or fourpoint bending tests and then used for determination of the compressive strength of concrete. Some concrete beams were reinforced, while others had no reinforcement. Accuracy of the experiments and calculations was verified in a non-linear analysis.

Durable Performance of Recycled Concrete Using Coarse and Fine Recycled Concrete Aggregates in Air Environment

The influence of synchronous use of coarse and fine recycled concrete aggregates on durable performance of recycled aggregate concrete (RAC) in air environment were determined. In this study, three series of concrete mixtures were prepared, in which the coarse recycled aggregate was used as 0%, 30%, 60% and 90% replacements of coarse natural aggregate and fine recycled aggregate as 0%, 10%, 20%, and 30% replacements of fine natural aggregate. Meanwhile, fly ash and slag were used as 15%, 25%, 35% and 45% replacements of cement, respectively. The carbonation depths, compressive cube strength, workability of RACs were tested. The experimental results showed that RAC with synchronous use of coarse and fine recycled concrete aggregates had satisfactory durable performance. When RAC was used as structural concrete in air environment, the optimum synchronous replacements are 60% for coarse recycled aggregate and 20% for fine recycled aggregate.