Journal of Materials & Construction

The effect of printing direction on strength of 3D printed concrete

2023-08-15T13:17:55+07:00

This paper presents experimental results on the influence of printing directions on the strength of 3D printed concrete (3DPC) using materials available in Vietnam. The experimental results show that the printing direction has a significant influence on the strength of 3DPC with and without fiber, in which the X-direction printing samples has the lowest strength, only about 30-40% of the compressive strength and 20-30% of the flexural strength of the casted samples. However, the strength of the samples in the Y and Z directions is higher, for example, about 60 - 70% of the compressive strength and 40 - 50% of the flexural strength of the casted samples. The addition of fiber enhances the strength of 3DPC, especially with higher fiber contents, and reduces the anisotropy in flexural strength of 3DPC at a later age, i.e. 28 days.

Bloating of fly ash-based lightweight aggregates

2023-08-15T13:17:55+07:00

The present work characterized two types of fly ash, one from pulverized coal combustion and the other from fluidized bed combustion. The effects of fly ash origins, raw mix proportions, and sintering temperatures on the bloating of lightweight aggregates were studied. The raw mixtures were calculated based on Riley's SiO2 – Al2O3 – fluxing composition diagram. The exothermic combustion reaction of a large amount of unburnt coal causes overheating, which results in boiling and abnormal bloating behavior. Besides, raw mixture compositions outside Riley's composition margin perform efficient bloating with most pore sizes from 0.5 to 1 mm. Hence, besides the fluxing content, one should consider the amount of unburnt coal in the fly ash in synthesizing lightweight aggregates.

Fly ash-based frit as a sintering aid for ceramic body

2023-08-15T13:17:55+07:00

Coal fly ash is characterized by high silica and alumina contents, making it suitable as a raw material for alumosilicate ceramics. However, direct use of fly ash reveals obstacles such as high porosity, black core, cracking, and swelling. This work synthesized frit by melting a mixture of fly ash, quartz, limestone, and soda. TG-DSC analysis showed that the glass transition point of the frit occurs at approximately 600 degrees Celsius. Ceramic bodies from raw mixes containing various frit amounts were prepared and characterized. The results showed that with 4% being frit, the firing temperature could be reduced by 30 degrees Celsius, along with decreased water absorption and increased flexural strength. Besides, no swelling, cracks, or black cores occur. These observations indicate that fly ash-based frit is viable a sintering aid in ceramic production.

Environmental factors of utilizing steel slag as building materials and backfill materials

2023-08-15T13:17:55+07:00

This study aims to present about national and international regulations, standards reletated to environment parameters when using steel slag as building materials and backfill materials. As a part of this research, environmetal tests were undertaken to determine the hazardous components, natural radioactivity and potential of leaching heavy metals of steel slag samples. The laboratory test results shown that steel slag is classified as a non-hazardous industrial waste. In terms of natural radioactivity, steel slags were found to pose no environmetal risks for use as building materials and backfill material. Although trace amount of heavy metals was found in steel slag components, leachable heavy metals analysis implied the low possibility of leaching issue for steel slag applications. To give out a comprehensive conclusion on the environment impact of the use of steel slag, further environmental tests under actual conditions need to be performed. However, this initial laboratory test results demonstrated that steel slags have a great potential for use as building materials and backfill material without environmetal risks surrounding the area of use.

The study of force-resistance of reinforced geopolymer concrete beam

2023-08-15T13:17:59+07:00

During the recent decades, the development of geopolymer concrete technology towards to produce an alternative construction material solution for replacing the Ordinary Portland Cement (OPC) concrete. Compared to traditional concrete, the products using geopolymer material can reduce the significant amount of carbon footprint and positively impact the environment. This study demonstrated that the flexural force-resistance of Geopolymer concrete (GPC) is higher than the OPC concrete, especially the higher flexural strength about 20% to 30%. Meanwhile, the Poisson's ratio and elasticity modulus of geopolymer concrete is equivalent to OPC concrete.

Experimental studying structural behavior of shear connector in cold-formed steel - concrete composite beam

2023-08-15T13:17:59+07:00

An experimental push-out test was carried out on 12 specimens in 6 groups to investigate the mechanical behavior of shear connectors in cold-formed steel-concrete composite beams. Specimen groups have differences in rivet spacing, shear connector spacing, tab aspect, and rebar through shear connectors. The mechanical behavior was evaluated through quantities such as shear resistance, relative slip between the steel beam and concrete slab, and failure modes. The results show that screw significantly affects the mechanical behavior of shear connectors in cold-formed steel-concrete composite beams.

The pounding mitigation techniques in adjacent structures due to earthquakes

2023-08-15T13:18:02+07:00

Investigations of past and recent earthquake damage have illustrated that the building structures are vulnerable to severe damage or collapse during moderate to strong ground motion. Among the possible structural damages, seismic induced pounding has been commonly observed in several earthquakes. Adjacent buildings during an earthquake may collide against each other when, owing to their different dynamic characteristics, the building vibrate out of phase and the at-rest separation distance is inadequate to accommodate their relative motion. When impact loads from pounding are too high, the structural system has to be modified to reduce the response. This research work covers the mitigation of pounding between adjacent structures due to earthquakes. The methods may be classified according to their approach to the problem of pounding: Methods to avoid pounding; Methods to increase the stiffness of building; Methods to supplement energy dissipation; Methods to impact absorb material.

Study on use the bottom ash from waste incineration plant as fine aggregate in manufacture of controlled low-strength materials

2023-08-15T13:18:06+07:00

This research investigates the manufacture and properties of controlled low-strength materials (CLSM) that were produced using bottom ash (BA) as fine aggregate (F). Mixtures of CLSM were prepared with various volume ratios of F-to-BA (100/0, 90/10, 70/30, and 50/50) and a constant amount of 5% cement, 10% slag, 82% fly ash and 3% CaCL₂. CLSM mixtures were prepared at an initial ratio of water to powder (w/p) of 0.35 and added water to obtain the flow of 30±2cm. The properties of CLSM were evaluated by relevant standards. The experimental results show that the flow of all CLSM mixtures met high flowability requirements under ACI 229R. Using BA as fine aggregate reduced the fresh unit weight of CLSM but delayed the setting time. Moreover, CLSM mixtures could serve as a re-excavation and pavement subbase.