High-strength Cement Concrete Research Articles

Determination of coefficient “s” and apparent activation energy for fib model code’s maturity-based strength function when applied to fly ash concrete

The maturity-based strength function recommended by fib model code 2010 can be easily utilized to estimate the compressive strength of normal-strength or high-strength cement concrete. However, the lack of calculation approaches and guidelines for determining the coefficient “s” and the apparent activation energy Ea in the fib model code’s maturity method have limited its further application to fly ash (FA) concrete. In this study, with reference to ASTM C1074, this limitation is addressed by adopting the equivalent mortar method to determine the coefficient “s” for the concrete under investigation. The feasibility and superiority of the equivalent mortar method were validated through two cases. Moreover, the original strength function in fib model code is modified to incorporate the reaction rate constant, allowing the use of Arrhenius equation to determine the mixture-specific Ea value. The iterative searching method is also supplemented to find the best-fit Ea value. The results demonstrated that the Ea value, obtained either through the linear Arrhenius plot or the iterative searching method, does not match the default Ea value (33.33 kJ/mol) provided by the fib model code, and can achieve relatively lower standard error for strength estimation of FA concrete.

JUSTIFICATION FOR THE BUILDING MATERIALS REQUIREMENTS IN THE ASPHALT PAVEMENT REPAIR BY THE CEMENT CONCRETE LAYERS

This scientific text examines the main requirements for the composition of cement-concrete mixtures for pavement layers. In particular, it is noted that to obtain high-strength cement concrete, type I and II Portland cement should be used with the content of tricalcium aluminate (C3A) in an amount of no more than 8% by weight. To increase the strength of concrete, it is recommended to add steel or polypropylene fiber. Coarse aggregate of high-strength modified cement concrete can be crushed stone from dense rocks. To obtain high-strength cement concrete, it is also necessary to take into account the requirements for sand, and entraining additives and calculate the composition of concrete in accordance with the methodology for road cement concrete. Ensuring the necessary frost resistance is achieved by selecting the optimal composition of the concrete mixture and using highly active cement. In addition, the text specifies the requirements for the transportation of the concrete mixture, the slump of the cone, the volume of entrained air, and the preservation of concrete properties. The final technological properties of the concrete mixture are evaluated at the design stage.

AN IMPACT OF THE STEEL-CONCRETE COMPOSITE SUPPORTING STRUCTURE ON THE DYNAMIC PARAMETERS OF THE MACHINING CENTER

A self-excited vibration, called “chatter”, is a main limiting factor in chip-forming metal machining. The reduction of machining productivity, worsened machined surface quality and the reduction of lifetime of the machine tool parts, particularly the cutting tool itself, occur as a result of the chatter. There are more ways to suppress this undesired effect of machining. The most common and simplest variant is the structural modification of the supporting parts of the machine in order to increase the dynamic stiffness and damping. In most cases, manufacturers of the machining centers use traditional metallic materials (steel, cast iron) for construction of the machine supporting system. However, these materials have some limitations. In order to improve the dynamic parameters of the machine during machining process it is appropriate to combine these materials with others to create hybrid, composite structures. Authors of this article have performed the real experiment in order to test the real dynamic properties of the vertical multitasking machining center with the turning operation prevailing. The individual segments of the supporting structure are made of the composite material – a combination of a steel welded structure filled with high-strength cement concrete.

Experimental Investigation of Engineering Properties of Iron-Based Binary and Ternary Pozzolanic Supplementary Cementitious Materials

The characteristic global warming potential of ordinary Portland cement (OPC) makes it a huge challenge for researchers to weigh its enormous use with potentially feasible engineering properties versus the environmental impacts. The formulation of sustainable, economical, and greener supplementary cementitious materials (SCMs) is an ongoing phenomenon, attracting the large-scale attention of industry/ academia. The formulation of ferrock by David Stone with low embodied energy, lower consumption of natural resources and minimal global warming potential has paved the way for the use of novel material comprising iron powder, pozzolans (pulverised fly ash (PFA) and metakaolin (MK) and lime exhibiting at par performance with OPC. However, a gap has been identified in its formulation, raising a further research question on how it will perform if PFA and MK are replaced by ground granulated blast furnace slag (GGBS) or other pozzolans like silica fume (SF) etc., with different mix ratios. Therefore, an endeavour has been made in this study to identify the engineering properties with sustainable use of modified binary and ternary pozzolans/ GGBS in place of 20% PFA in conventional ferrock. The conventional ferrock contains 8% MK and 20% PFA (as binary pozzolans), 60% iron powder, 12% lime and 2% oxalic acid (set 1). An effort has been made to formulate the different mixes of 10,20,30,40 and 50% by keeping 60% iron powder, 12% lime, 8% MK and 2% oxalic acid constant but replacing 20% PFA with 20% GGBS (set 2), with 10%PFA+10%GGBS (set 3) and with 10%PFA+10%SF (set 4). A target compressive strength of C32/40 or M40 concrete was selected for this study to achieve and compare results with the control mix (0% ferrock) and conventional ferrock during the experimental investigation of modified novel materials. 10-20% ratios of modified mixes exhibited the best performance and achieved the threshold strength of 60 MPa of high-strength cement concrete. Maximum compressive strength of 65 MPa was achieved by the 10% mix of set 2 (20% GGBS), followed by 20% mix ratios of set 3 (10%PFA+10%GGBS) and set 4 (10%PFA+10%SF), achieving 64 MPa. Whereas the 10% mix of the conventional ferrock (set1) reached 63 MPa strength, and the control mix with no ferrock gained 57 MPa strength at 56 days of curing. Overall, an increase of 2-13% compressive strength was observed with10- 30% mixes of all the SCMs; however, a decrease of 3-27% was observed with 40-50% use of SCMs. The use of iron powder increased the ductility of ferrock-based SCMs mixes and exhibited more flexural strength. Set 3 performed the best in exhibiting up to 5.8 MPa flexural strength, followed by set 4, set 2 and lastly, set 1 of conventional ferrock. 20% and 30% mix ratios exhibited flexural strength of more than 5% MPa, better than 10% and 40/ 50% mixes. The study supports the use of 10-20% ferrock-based SCMs for high-strength concrete and 10-50% for concrete mixes with a target strength of C32/40 or M40 to decrease the CO2 footprints of the construction industry significantly.

Compression behavior and modeling of FRP-confined high strength geopolymer concrete

Fiber-reinforced polymer (FRP) has proven its efficiency as a strengthening material of ordinary concrete. However, the research on the effect of these materials on geopolymer concrete is still less understood. Due to the excellent mechanical and environmental properties of geopolymer concrete, the compression behavior of confined high strength geopolymer concrete (HSGC) is experimentally and analytically investigated and compared with high strength cement concrete (HSC). The confined cylindrical test specimens of HSGC and HSC were tested in compression. The cylinders were confined using three schemes of FRP, namely one and two layers of Glass FRP (GFRP) and one layer of carbon FRP (CFRP). The stress–strain behavior of the HSGC is compared with HSC for different levels and types of confinement. For low confining pressure, there was a definite peak followed by descending portion of the stress–strain curve, whereas for high confining pressure, initially, the stress increases nonlinearly with strain, and after reaching a certain level of stress, it becomes asymptotic to a positive slope straight line. A single equation is proposed for predicting all curves of HSGC and HSC for low as well as high confining pressures. The validation of the model is also successfully shown with the data taken from the literature for a wide range of confinement levels.

Development of Alkaline Activated High Strength Concrete using Fly Ash - Ground Granulated Blast Furnace Slag - Metakaolin as Binders and Manufacturing Sand as Fine Aggregate

Structures built with normal concrete are fading out from the construction industry due to the development of high strength concrete. The massive structures such as sky scrapers, bridges, tunnels, nuclear plants, underground structures need high strength concrete to withstand the high intensity vertical, horizontal and moving loads etc. The development of high strength alkaline activated concrete will reduce the usage of cement in construction community. Lesser the utilisation of cement will lessen the high emission of carbon dioxide gas into the atmosphere. In this study, high strength concrete using alumina and silica rich materials are made with a mix ratio of 1:1.31:2.22. The water to cement ratio for high strength cement concrete and the alkaline solution to binder ratio for alkaline activated concrete are kept as 0.35. Low calcium fly ash, Ground Granulated Blast Furnace Slag (GGBS) and Metakaolin are used as binders and Manufacturing Sand is used as fine aggregate to made high strength alkaline activated concrete. The high strength alkaline activated concrete tests results are better than the high strength cement concrete.

A Study on High Strength Geopolymer Concrete with Alumina-Silica Materials Using Manufacturing Sand

High strength concrete is an essential need for construction industry since the importance of the structures are of a deep concern. Concrete is said to be high strength concrete (HSC) when the compressive strength exceeds 55 N/mm2. Due to the vast infrastructure development around the world, the need for high strength concrete is increasing day by day. Nowadays, in the construction industry the environmental conditions, types of structures, availability of materials and effect of greenhouse gases in the past were not as same as today. The structures built today have to face a lot of challenges to withstand the hysterias effects. Nowadays the infrastructure development increased by constructing innovative structures in the aspects of size and shape. Presently the architects are keen in constructing lean structures to increase the aesthetic looks of the structure. For the construction of such innovative structures, high strength concrete is essential. On the other hand, the availability of the materials for cement concrete and the emission of carbon dioxide to atmosphere due to the production of cement are the serious issues emerging in the construction industries creating major problems regarding environmental safety conditions. This study is mainly concentrated to produce high strength concrete with sustainable materials without cement to find a solution to the above problems. This is achieved by using geopolymer concrete with alumina-silica materials, made up of fly ash, Ground Granulated Blast Furnace Slag (GGBS), Manufacturing Sand (M Sand), crushed stone aggregate and alkaline solution. In this study high strength geopolymer concrete with and without Manufacturing Sand is considered for research and the results obtained are compared with high strength cement concrete with and without Manufacturing Sand. In this study river sand is completely replaced with M Sand. The use of Manufacturing Sand in the concrete contributes to the strength due to its better gradation.

Abrasion resistance of sustainable green concrete containing waste tire rubber particles

The development of new environmental friendly concretes such as rubberized concrete is being promoted due to the environmental problems created by the waste tire rubber. Every year millions of tires are discarded, thrown away or buried all over the world, representing a very serious threat to the ecology. In this study, we analyse the potential of waste tire rubber particles as a partial substitute for fine aggregates in normal strength and high strength cement concrete and the resistance to abrasion has been measured. Statistical Analysis was carried out to strengthen the results obtained from experiments. The results show that the use of tire rubber particles can improve the abrasion resistance of concrete, and this can ensure its applications in pavements, floors and concrete highways, or in places where there are abrasive forces between surfaces and moving objects.

Properties of high strength concrete containing scrap tire rubber

Disposal of waste tire rubber has become a major environmental issue in all parts of the world representing a very serious threat to the ecology. One of the possible solutions for the use of scrap tire rubber is to incorporate it into concrete, to replace some of the natural aggregate. This paper presents the results of an experimental research to analyse the suitability of scrap tire rubber as a partial substitute for natural fine aggregate in high strength cement concrete. Crumb rubber replaced natural fine aggregate from 0% to 20% in multiples of 2.5%. Tests were performed to determine the compressive strength, flexural tensile strength, pull-off strength, abrasion resistance, water absorption and water penetration of these concrete samples and their microstructures were observed using Scanning Electron Microscopy (SEM). It was observed that the compressive strength, flexural tensile strength, pull-off strength and depth of water penetration of the rubberized concrete were less than that of the control mix, while the abrasion resistance and water absorption (up to 10% substitution) exhibited better results than that of the control mix concrete. Rubberized concrete may be used in structures where there are chances of brittle failure. Crumb rubber may be utilized in high strength concrete as a partial substitute for fine aggregate up to 12.5% by weight for obtaining strength above 60 MPa.

Performance of high strength rubberized concrete in aggressive environment

Due to the huge increase in the population and number of vehicles, lots of tyres are ending as waste every day. It was estimated that every year almost 1000 million tyres end their useful life and more than 50% are discarded without any treatment. One of the possible solutions for the effective use of waste tyre rubber is to incorporate into cement based materials, to replace some of the natural aggregates. In this study, waste tyre rubber in the form of crumb rubber was used as a partial replacement for natural fine aggregates in high strength cement concrete. Crumb rubber was replaced for fine aggregates from 0% to 20% in multiples of 2.5%. Tests were done to determine the depth of carbonation, water absorption of acid attacked specimens, compressive strength of acid attacked specimen, variation in weight of acid attacked specimen and chloride penetration of these concrete samples. From the test results it could be concluded that the high strength rubberized concrete are highly resistant to the aggressive environments.

Flexural rigidity and ductility of high-strength reinforced polyester polymer concrete beams

The structural behaviours were analysed for reinforced polymer concrete. The analysis included load–deflection and moment–curvature responses, ductility index, and flexural rigidity. Ductility indexes computed on the basis of deflections and curvatures were higher than those of high-strength cement concrete. The prediction equation for the effective moment of inertia proposed by ACI 318 is not applicable to high-strength polymer concrete, because the ACI 318 equation does not reflect the high effective moment of inertia of high-strength polymer concrete. Therefore, an empirical equation was proposed to estimate the effective moment of inertia of simply supported reinforced polymer concrete beams. The predicted deflections using the proposed formula agree well with the experimental deflections of the tested polymer concrete beams.