Materiales de Construcción

Ultramarine blue pigment degradation in cementitious materials: a new approach to the phenomenon

2023-07-03T08:42:39+02:00

The paper analyses the degradation process of commercial ultramarine blue pigments in cementitious materials. For this purpose, two commercial pigments (with and without a protective coating) in different solutions and cement pastes are studied incrementally. The results show that pigment degradation occurs due to an ion exchange phenomenon; during hydration high ion contents are released, calcium and potassium being the most aggressive for the pigment. Calcium distorts the unit cell; between the sodium of the pigment and the potassium in the medium a cation exchange phenomenon takes place. Both processes lead to the diffusion of sulphate and sulphide ions from the pigment to the medium causing loss of colour and the formation of ettringite.

Shear strength and microstructural investigation on high-volume fly ash self-compacting concrete containing recycled concrete aggregates and coal bottom ash

2023-05-25T23:47:33+02:00

This article presents the experimental outcomes of the shear strength and microstructural characteristics of high-volume fly ash self-compacting concrete (HVFYA-SCC) containing recycled concrete aggregates and coal bottom ash as partial replacements for natural coarse aggregates and natural fine aggregates. A total of ten numbers of mixes were produced, including HVFYA-SCC made without recycled concrete aggregates and coal bottom ash (as control) along with HVFYA-SCC mixes made with recycled concrete aggregates (from 25% to 50%) and coal bottom ash (from 10% to 30%). The compressive and shear strength of the HVFYA-SCC mixes were improved by 7% and 4%, respectively, with the incorporation of 20% coal bottom ash and 25% recycled concrete aggregates after 120 days of curing. On the other hand, scanning electron microscopic analysis revealed that incorporating coal bottom ash exhibited the pozzolanic reactions with fly ash densified the binder-aggregate matrix of the resulting HVFYA-SCC.

Investigation of the bond properties between hybrid fiberreinforced concrete and BFRP bars after exposure to high temperature

2023-10-21T21:29:06+02:00

This research investigated the bond properties at high temperatures and with hybrid fiber addition between basalt fiber reinforced polymer (BFRP) bars and hybrid fiber-reinforced concrete (HFRC). The tensile strength and appearance morphology of BFRP bars were analyzed. Used scanning electron microscopy (SEM) to examine the microscopic morphology and used the bond-slip constitutive model to fit the bond-slip curves. When BFRP bars after exposed to 300 °C, their tensile strength dropped by 42%. With the increasing temperature, the bond strength and stiffness of normal concrete (NC) specimens decreased by 27.3 % and 67.5 %, respectively, while HFRC specimens decreased by 20.8 % and 55 %, respectively. Hybrid fibers increased the bond strength and stiffness of HFRC specimens by 27.1 % and 49.1 %, respectively. The best fitting models were the Malvar model and the Continuous Curve model.

Life cycle analysis and economic evaluation of cement and concrete mixes with rice husk ash: application to the Colombian context

2023-07-04T10:47:51+02:00

Rice husk residues are generated within the rice industry. In this research, the environmental impact of the use of rice husk ash is evaluated as a replacement for cement in the production of concrete in the city of Ibagué (Colombia). The environmental criteria of cement and concrete production alternatives were evaluated through life cycle analysis methodology, using SimaPro 9.3.3 software and the Recipe 2016 Midpoint (H) evaluation method. The economic cost of each of these production alternatives was included. To carry out the study, surveys and interviews had to be undertaken with rice-producing plants, aggregates, cement and concrete plants in Tolima. It was corroborated that rice husk ash (RHA) generated during the rice husk (RH) gasification process for electricity and heat production was beneficial from an environmental and economic perspective when it was used in cement and concrete in the city of Ibague (Colombia).

Influence of crystallizing type chemical admixture on precast micro concretes: a statistical analysis and holistic engineering overview

2023-07-12T14:53:10+02:00

The aim of this paper is to evaluate the influence of a crystallizing chemical admixture on precast micro concretes with two water contents (7% and 11%, by dried mass) and two different conditions of exposure. Thus, precast micro concretes with a composition of 1:3 (cement: fines) with and without crystalline chemical admixture were evaluated on compressive strength (at the age of 28 and 154 days) and water absorption by immersion (at the age of 154 days). Statistical analysis showed that the only significant factor was the effect of the water content on the compressive strength. Besides that, the most significant factors for the water absorption and voids index properties were the water content, followed by the exposure conditions, and the interaction between the water content and the presence of the chemical admixture. The crystalline admixture was insignificant in the conditions of this research.

Structural aspects of concrete incorporating recycled coarse aggregates from construction and demolished waste

2023-08-16T16:16:45+02:00

The study explores the potential of recycling construction and demolition waste into recycled coarse aggregates (RCA) to decrease waste generation and carbon footprint, using a standard compacting effort to calculate compressive strength and particle packing density in a specific cylindrical volume. This study investigates the impact of RCA on concrete’s workability, compressive strength, flexural, split tensile, drying shrinkage, electrical resistivity, rapid chloride penetration, and microstructural characteristics using XRD, SEM, and EDAX. Test findings showed that increasing the replacement percentage beyond the optimum value (RCA 25) had detrimental effects on the strength and microstructure of the concrete. RCA 25 has a higher compressive, flexural, and split tensile strength in the order of 11.56%, 3.06%, and 5.17% respectively compared to reference concrete, as well as 5.23% increase in drying shrinkage, 8.79% higher electrical resistivity, and 4.68% higher resistance to chloride penetration than reference concrete.

Durability effect of reclaimed asphalt aggregate on concrete road pavement

2023-07-17T14:52:08+02:00

The use of recycled aggregates instead of natural aggregates used in concrete reduces environmental pollution and concrete costs. Recycled Asphalt Pavement (RAP) aggregate used as recycled aggregate has a lower water absorption than natural aggregate due to its bituminous structure, which reduces the water requirement of fresh concrete. In this study, it was aimed to determine the optimum use of RAP particles as aggregate in concrete for read pavements and to determine their durability properties. For this purpose, RAP was used instead of crushed stone aggregate used in concrete road construction. RAP was used by replaced aggregate 0%, 25%, 50% and 100% of the crushed stone aggregate used on the concrete road. The dose of the produced concrete was 350 kg/m³ and the water/cement ratio was kept constant as 0.45. The fresh workability and air content of concretes containing RAP were determined. Compressive strength, splitting tensile strength, electrical resistivity value, accelerated corrosion test of hardened concretes were subjected to corrosion resistance, water absorption and porosity percentage, acid resistance, ultrasonic pulse rate and Scanning Electron Microscope (SEM) and X-ray Diffractometer (XRD) analyzes were determined. In the experimental results, it has been observed that the use of RAP ratio of 25% and 50% remains within the limit values for concrete pavement. It is recommended to be used on reinforced concrete roads that will be exposed to adverse environmental conditions with its high corrosion resistance, thanks to its anti-corrosion feature.

Experimentation and numerical analysis of the influence of geogrids with emulsion insertion on the behavior of bituminous pavements - Case of Ouargla aerodrome

2023-09-08T22:54:36+02:00

This paper presents an experimental study on a set of 30 specimens, tested on three-point bending, divided into two categories. With the insertion of geogrids and cathodic emulsions, the first category consists of 14 prismatic beams and the second of 16 pre-cracked and reinforced slab specimens. In situ tests were carried out using a heavy deflectometer (HWD) on a flexible runway of an airfield located in the city of Ouragla (800 km south-east of Algiers), before and after its reinforcement. This work showed, with a numerical calibration, that the geogrid with emulsion, improves the displacements and the stresses approximately 30% and increases the modulus of elasticity and the modulus of rupture (MOR) by 60% and 20%, respectively. The damping coefficient (k) can reach the value of 2 to 5, which increases the longevity of a reinforced flexible pavement.