Pore Structure Of Foam Concrete Research Articles

Assessment of pore structure of foam concrete containing slag for improved durability performance in reinforced concrete applications

The traditionally produced foam concretes (FCs) for light-weight applications have a high air void content of about 10%–60%, are characterized by significant void connectivity, and hence are unsuitable for reinforced concrete applications. Since void connectivity in FCs can pave the way for the entry of external solutions inside their matrices and reach the steel reinforcement, designing such mixtures for durability requires significant attention. The approach is to develop FCs with appropriate GGBS dosages and foam additions that can provide optimum density and strength levels, discontinuous pore structure, and durability characteristics that are sufficient to replace conventional concrete. The main goal is to understand the effect of GGBS addition on the pore structure of FCs. Five different FC mixtures were prepared with 0%, 15%, 30%, 45%, and 60% GGBS dosages as a replacement of cement, and their pore structure aspects were studied using image analysis, scanning electron microscopy (SEM), and mercury intrusion porosity (MIP). Based on the durability test results, the water absorption, porosity, chloride ion permeation, resistivity, and drying shrinkage values decreased with increasing GGBS dosage up to 60%, whereas sorptivity decreased with increasing GGBS dosage up to 30%. Images from image analysis and SEM indicate that the macrovoids created are isolated and discontinuous in nature. Further, SEM images reveal that the addition of up to 60% GGBS improved the microstructure and void structure of FCs. The MIP results indicate that the decrease in porosity of FC was noticeable up to 30% GGBS dosage, with lowered threshold and critical pore diameter values and higher amounts of gel pores. However, 60% of GGBS dosages showed reverse trends. The MIP and SEM results supported the trends obtained with most durability tests up to 30% and 60%, respectively. Overall, the dependence of FC durability on the pore size and pore structure of cementitious matrices is evident, and the potential for developing FC mixtures with enhanced durability seems promising.

Alkali-activated fly ash foam concrete with Yellow River silt: Physico-mechanical and structural properties

Developing innovative techniques to elevate the utilization efficiency of the Yellow River silt (YRS) is very important for the protection of the Yellow River in China. In this study, an approach to use the YRS in the fabrication of alkali-activated fly ash (AAFA) foam concrete was first attempted, and YRS was used as a kind of supplementary binder material. The effects of silt dosage and alkali content on the fluidity, water absorption, compressive strength, drying shrinkage and thermal conductivity of as-fabricated foam concrete with YRS were examined. Besides, the characteristic of pore structure and microstructures of foam concrete were characterized. The results show that the incorporation of YRS significantly affects the physico-mechanical properties of the AAFA foam concrete. With the increase of YRS dosage, the fluidity of fresh foam concrete and the dry density, mechanical properties, thermal conductivity and drying shrinkage of hardened foam concrete is reduced. However, the water absorption and pore structure of foam concrete is improved. In addition, the change of Ca(OH)2 content has a great influence on the physico-mechanical and structural properties of AAFA foam concrete. With the increase of Ca(OH)2 dosage, the dry density and thermal conductivity of AAFA foam concrete is increased obviously. Furthermore, the main hydration product of the AAFA foam concrete with YRS is C-S-H gels. The overall findings demonstrate the feasibility of using YRS as dependable and cost-effective building materials in the preparation of AAFA foam concrete.

Study on novel steel slag foam concrete pore structure and bp neural network prediction model

In this paper, a new type of steel slag foamed concrete was prepared. Its pore structure was analyzed by MATLAB image processing technique, and the influence of steel slag on the compressive strength of foamed concrete was investigated. In addition, a BP neural network prediction model for the pore structure of foam concrete was established. The research results show that when the content of steel slag is 30%, the pore structure of steel slag foamed concrete is appropriate. The compressive strength of steel slag foamed concrete increases with the decrease of the density and the proportion of irregular pores. With the density remaining unchanged, the compressive strength of foamed concrete increases with the increase of the ratio of round and small pores. The prediction errors of the BP neural network model in the average pore diameter and average pore roundness factor were less than 8.5% and 5%, respectively.This research can provide a theoretical basis for the production of steel slag foam concrete.

Effect of formic acid as an accelerator on foam-stability, compressive strength, and pore size distribution of foam concrete

In this study, the formic acid as an accelerator was used to increase the properties of the foamed concrete. The impact of formic acid on the performance of foam concrete was investigated experimentally. The experimental results reveal that using formic acid as an accelerator can significantly increase the rate of yield stress evolution in the matrix. The matrix with the higher yield stress evolution rate tends to increase the stability of the fresh foam concrete. In addition, the –COOH in formic acid can absorb the moisture in the foam, thus increasing foam drainage. The excess formic acid in the base mix can reduce the stability of the fresh foam concrete. The compressive strength of foam concrete can be significantly increased with the addition of 1.0% formic acid. A more homogeneous and finer pore structure of foam concrete can be obtained with the incorporation of 1.0% formic acid, which may result in lower water absorption and higher compressive strength.

The effect of lithium silicate impregnation on the compressive strength and pore structure of foam concrete

Foam concrete (FC) has been widely used to make slab structures, retaining walls, and backfill materials for highways, railways, plazas and other projects due to its high flowability, low cement content, cost reduction, and thermal insulation. However, the low compressive strength and durability of FC limit its further application in structural materials. This paper focuses on improving the compressive strength and freeze-thaw cycle (FTC) resistance by adjusting the pore structure. The method proposed in this paper utilizes calcium silicate hydrate gel (C-S-H) formed by the rehydration reaction between lithium silicate (LS) and calcium hydroxide (CH). In this paper, the FC samples were treated by LS solution impregnation for 6 h. LS's effects on the dry density, 7- and 28-day compressive strength, strength-to-weight ratio (S/W ratio), and FTC resistance were studied. The results show that LS enhances the properties of FC, including the S/W ratio, compressive strength, and FTC resistance. In particular, the growth rate of the sample's compressive strength varies between 4.8% and 59.5%. The growth rate of the compressive S/W ratio was between 27.0% and 52.0%. The FTC resistance is improved. Thermogravimetric (TG) analysis and pore structure analysis results show that a rehydration process to generate C-S-H was observed between CH and LS, which can optimize FC's pore structure.

Water transport in foam concrete: visualisation and numerical modelling

Most problems concerning the durability and functional degradation of foam concrete are intimately related to water transfer. The water transfer behaviour in foam concrete under capillary absorption and full submersion conditions is studied in this paper. To overcome the low resolution between water and cement paste in in-situ X-ray computed tomography (XCT) tests, caesium chloride (CsCl; 6 wt%) was used as a contrast-enhancement agent. The dynamic changes to the wetting head and water distribution in foam concrete were successfully visualised in two and three dimensions. The multiscale pore structure of foam concrete was quantitatively characterised by a combination of mercury intrusion porosimetry (micropore <10 μm) and XCT (macropore >10 μm). The results show that the microporosity governs a large part of the capillary suction of water due to the high capillary force in these micropores. However, for macropores, they are partially connected and can hold water under pressure and simultaneously hinder capillary rise due to the blocking of the capillary network and prolonged transfer tortuosity. Finally, a numerical finite-volume model was used to simulate the dynamic water transfer process directly based on the XCT binary images. The modelling results agreed well with the experimental results.

Impact of Superplasticizing Agents on Physical and Mechanical Properties of Cellular Concrete

The effect of superplasticizing, foam agents, various fiber aggregates on the physical and mechanical properties of cellular concrete has been studied. The article covers the results of experimental studies conducted to determine the effect of foam agents PO-6 and PB-2000, as well as polymeric and basalt fiber on the pore structure of foam concrete. The dependence between the change in density and strength of cellular concrete and the structure of its pore space has been determined.

Experimental study on pore structure and mechanical property of chemical foaming foam concrete

In this paper, foam concrete (FC) was prepared by chemical foaming method. Besides, the effects of different density grades and fly ash content on the pore structure of FC and the mechanical response of FC under static and dynamic forces were discussed. At the same density grade, the FC strength shows the feature of first increasing and then decreasing with the increase of fly ash production. The pore diameter of FC prepared with protein foaming agent is between 60-800µm, with the uniform pore distribution. The higher the density grade, the smaller the proportion of irregular pores in the FC and the larger the proportion of round pores.When the fly ash content is relatively small, the pore diameter inside the concrete can be significantly reduced, and the pore shape develops more like a circle. When the external dynamic strain rate increases from 10-5/s to 10-3/s, the uniaxial compressive strength of the FC test sample increases by about 14.1%, and the triaxial compressive strength increases by about 61.9%. Therefore, FC exhibits typical ductile failure characteristics under dynamic stress, which can significantly delay the impact of dynamic loads such as earthquakes and explosions. This is of great significance for the engineering application of FC.

Influences of Polypropylene Fiber on Properties of Foam Concrete with Iron Tailings

Iron tailings are mineral wastes obtained from industrial processing and magnetic separation of iron ore. Foam concrete with iron tailings can be made with iron tailings, cement, fly ash, silica fume, polypropylene fiber, superplasticizer, early strength agent, accelerating agent and foaming agent. The influences of polypropylene fiber on the crack resistance and frost resistance of foam concrete have been investigated in this study. Further, the microstructure of foam concrete was observed. This result demonstrates that polypropylene fiber has greatly increased the crack resistance and frost resistance of foam concrete. The pore structure of foam concrete is improved obviously by polypropylene fiber. Due to the uniformly distributed pores, high porosity and rather complete pore wall, the mechanical properties and thermal properties of foam concrete are excellent. The foam concrete with high-strength and excellent thermal insulation property develops a new route for the comprehensive utilization of iron tailings.