Materiales de Construcción

The effect of recycled concrete powder (RCP) from precast concrete plant on fresh and mechanical properties of cementitious pastes

2023-04-04T09:55:29+02:00

This study aims to evaluate the effect of RCP from a precast concrete plant on rheological and mechanical properties of cementitious pastes. In the study, Portland cement was replaced by RCP in 10, 20, and 30% (in mass). The hydration kinects of cement with RCP was studied through isothermal calorimetry. The fresh properties were assessed using mini-slump test and rotational rheometry. The mechanical properties were evaluated through compression tests and the microstruture was studied using Scanning Electron Microscopy. RCP reduces fluidity of the pastes, by increasing both yield stress and plastic viscosity. The addition of RCP accelerates the hydration of cement, while reducing the released heat. RCP also reduces the compressive strength and elastic modulus of the pastes. The use of RCP as partial substitute for cement is viable, due to its size distribution and specific surface area.

A low carbon cement (LC3) as a sustainable material in high strength concrete: green concrete

2023-05-04T18:31:22+02:00

Limestone Calcined Clay Cement (LC₃) Technology is a low carbon cement that combines limestone, calcined clay, and clinker, aiming to reduce CO₂ emissions by 40%-50% during production. In this study, large-scale investigations were conducted to explore LC₃ as a potential substitute for conventional cement (CC). Mechanical and durability tests were performed on LC₃, comparing results with CC and Pozzolana Cement (PC) concretes. The findings revealed that LC₃ concrete exhibited promising early-stage strength similar to CC concrete. However, at 90 days, LC₃ showcased a 10% higher strength compared to CC concrete. Additionally, LC₃ displayed a remarkable 45% increase in resistance to moisture ingress, indicating improved durability over CC concrete. These results highlight the efficacy of low carbon cement in developing ternary blended cements that offer early strength and enhanced durability, making it a viable eco-friendly alternative in the construction industry.

Exploring the impact of graphene oxide on mechanical and durability properties of mortars incorporating demolition waste: micro and nano-pore structure effects

2023-05-18T17:41:11+02:00

In this study is explored the use of construction and demolition waste as fine aggregate in mortars. The addition of nano-graphene oxide (0.1%wt) has also been evaluated. Tests were conducted to determine their density, humidity content, water absorption capacity and open void porosity (using water absorption) and the micro and nano-porosity using Hg intrusion and N₂ absorption techniques, as well as their flexural and compressive strength and resistance to acid attacks. The mechanical properties of mortars manufactured with standard sand were better (30%) than made with waste aggregate. Mortars with both aggregates can be classified as M20. Nano-Graphene oxide acts as a filler, reducing the volume of macro and micro pores, thereby increasing the mechanical performance, especially when recycled aggregates are used (30% the flexural strength for recycled aggregates and 4% for standard sand). The addition of nano-graphene oxide reduces the transmission channels of acid within mortar.

Effect of fiber section shape and volume fraction on the mechanical properties of steel-fiber reinforced concretes

2023-04-26T16:15:12+02:00

This study presents the preparation of steel-fiber reinforced concretes (SFRCs) using straight navicular fibers with annular-sector-shaped sections and corrugated fiber with rectangular-shaped sections, respectively. The flexural and splitting tensile strengths of both the respective SFRCs increase with increasing fiber volume fraction, whereas their compressive strengths initially increase, then decrease, and then increase again. For the same fiber volume fraction, the mechanical properties of the navicular fiber-reinforced concrete are superior to those of the corrugated fiber-reinforced concretes. The introduction of steel fiber changes the failure mode of the plain concrete during bending from a typical brittle mode to a bimodal ductile failure mode. As compared to the corrugated fiber, the navicular fiber has stronger interface bonding to concrete and a higher friction resistance to fiber sliding and subsequent pullout. Furthermore, navicular fiber has a higher load-bearing capacity, which makes it more favorable for improving the mechanical properties of plain concrete.

Experimental investigation of the behavior of concrete beams containing recycled materials reinforced with composite rebars

2023-09-05T17:07:56+02:00

The application of various Fiber Reinforced Polymer (FRP) composite materials is very widespread in the world. The use of recycled materials in concrete, can improve some of the mechanical properties of concrete. In this laboratory research, the behavior of reinforced concrete beams with composite rebars with glass fibers made of concrete containing recycled materials such as glass, rubber and micro-silica with different mixing plans has been investigated. These mixing plans are such that recycled glass and rubber aggregates have replaced a percentage of fine and coarse concrete aggregates, and glass powder and micro-silica have also replaced a percentage of concrete cement. The results showed that the replacement of coarse rubber, glass powder, and micro-silica in concrete materials increases the bending strength and ductility of concrete beam. In examining the microstructure of concrete by Scanning Electron Microscope (SEM) the adhesiveness of the rubber Interfacial Transition Zone (ITZ) in concrete was suitable.

The effect of water absorption distribution of recycled coarse aggregate on the compressive strength distribution of high-performance concrete

2023-03-21T16:14:30+01:00

High water absorption is a typical characteristic of recycled coarse aggregate and is often used to explain the loss of performance of concrete when replacing natural coarse aggregate with recycled coarse aggregate. Extensive attention has been paid to the mean value of the water absorption of recycled coarse aggregate, but not to the standard deviation. This paper aims to assess whether recycled coarse aggregates with the same mean water absorption but different standard deviations will perform equally in high-performance concrete (HPC). The resulting HPC mixtures exhibited very similar compressive strength. Even so, it was hypothesised that as the standard deviation of the water absorption of recycled coarse aggregate increases over a wide range, the compressive strength of HPC will first increase due to local variations in the water/cement ratio, then decrease due to the presence of weak particles, and finally remain constant due to the role of the surrounding new mortar.

Eco-efficient thermoacoustic panels made of totora and gypsum for sustainable rural housing ceilings

2023-03-24T12:34:26+01:00

The energy deficiency in rural housing in the Andes of Peru is recurrent. In this context, local and low environmental impact materials present an opportunity. This research evaluated the properties of five panels composed of totora and gypsum for ceiling applications. Firstly, the physical and durability properties were obtained. Then, impact and fire resistance were evaluated. Finally, thermoacoustic properties were assessed. The results showed a moisture level of 10.25%, water absorption of 354.85% which is considered high, and a dry density of 292.84 kg/m³. Adequate durability to fungus with resin on both sides. The panels’ fire resistance is superior to 60 minutes, with a safe impact criterion for 10 N and a functionality criterion for 5 N. The average values for the panels were 0.061 W/m·K for thermal insulation and 0.54 for NRC. Therefore, it is possible to produce an insulating material for thermoacoustic improvement.