A simple optimized foam generator and a study on peculiar aspects concerning foams and foamed concrete

This paper presents a study on peculiar aspects influencing foams and foamed concrete properties, starting from the foam generation up to the compressive strength of the lightweight and ultra-lightweight cementitious material. In particular, after a brief introduction on foam stability, this research work shows a simple and inexpensive foam generator used to produce the commonly used foams in concrete. The significant influence of the air pressure value, of nature and concentration of the foaming agents on density as well as the percentage drainages of the foams produced are therefore discussed. The results show that foams generated with the protein foaming agent have more suitable characteristics to produce foamed concrete, thanks to the significantly longer lifetime compared to foams produced with the synthetic foaming agent. The latter are characterized by very high drainage values even after a few minutes from their generation. Foams are then used to make lightweight (target dry density equal to 600 kg/m3 and 800 kg/m3) and ultra-lightweight (target dry density of 400 kg/m3) foamed concretes that show interesting results in terms of stability also when foams with high drainages are employed. The study provides explications of the differences between the compressive strength of lightweight foamed concrete obtained with foams generated using protein and synthetic foaming agents. Then, the significant influence of the increase in concentration of protein foaming agent on the compressive strength of ultra-lightweight foamed concretes is presented

Biochar addition for 3DCP: a preliminary study

This contribution presents the first results of an ongoing research aimed at highlighting the possible reduction in the environmental impact of concrete through the synergy between two interconnected strategies: the exploitation of by-products, in this case biochar, for the realization of 3D printable cementitious conglomerates. Thanks to the use of biochar, the mixes presented are characterized by an excellent dimensional stability in the fresh state, evaluated through the extrusion test. Regarding the hardened state properties, the contribution highlights the effects of biochar-to-cement ratio, water-to-cement ratio (in combination with biochar content) and sand-to-cement ratio on the flexural and compressive strength of the mixes. The evaluation of CO2 emissions shows that a proper mix design could result in a significant reduction in CO2 emissions (up to 43%) while maintaining good mechanical performance (compressive strength of at least 60 MPa)

Increase the fracture energy of foamed concrete: Two possible solutions

The aim of the present paper is to investigate the influence of the curing conditions and the addition of an eco-friendly filler, biochar, on the flexural strength and fracture energy of a "green" special concrete characterized by lightness, high thermal and acoustic insulation properties and excellent fire resistance: foamed concrete. The study aims to highlight the properties of this promising material that, depending on its density, can be used for both structural and non-structural purposes. In fact, if the material is designed with a density not exceeding 800 kg/m3, it can be employed in interior partitions or in high energy-efficiency building envelopes; on the other hand, if the material is designed with a density greater than 1400 kg/m3, it can be used for structural purposes. All this makes it legitimate to state that it is a material that can be engineered according to specific needs. In this contribution the possibility to improve the fracture energy through biochar addition in this special concrete is also analyzed and presented. In particular, two different dry density were investigated: 800 kg/m3, and 1600 kg/m3. The first one for non-structural applications, the second for structural purposes. With regard to the biochar, used for 1600 kg/m3density, two different percentages, 2% and 4%, were investigated. Two different curing conditions were analyzed, namely in air at 20°C, wrapped in cellophane at the same room temperature and cured in water at 20 °C. Three-point bending tests in CMOD (crack mouth opening displacement) mode and compressive tests on the two-halves of the broken specimens have shown interesting results. Curing conditions significantly affect the fracture energy and the addition of biochar at 2% concentration seems to be beneficial in improving the fracture behavior of foamed concrete

Key factors affecting the compressive strength of foamed concrete

This contribution aims to highlight, from an experimental point of view, the key factors affecting the compressive strength of foamed concrete. An experimental campaign has been conducted on a broad group of cubic specimens made of foamed concrete under compression tests at 28 days. In addition to the obvious influence of the density on the achievement of the compressive strength, other factors have been studied. In particular, three different curing conditions, three foaming agents with either synthetic or protein nature, two different cement types, and three water/cement ratios have been included in this experimental investigation. As a result of this experimental campaign, it has been found that the not only the density, but also the foaming agent and the water/cement ratio play a major role in the strength achievement of the foamed concrete. It is also demonstrated that the combination of the foaming agent with a particular water/cement ratio is a crucial parameter affecting the compressive strength of this material

Investigation on the compressive strength and durability properties of alkali-activated slag mortar: Effect of superabsorbent polymer dosage and water content

This paper presents the properties of alkali-activated slag (AAS) mortar additivated with a superabsorbent polymer (SAP) to improve its mechanical and durability properties. The effect of different dosages of SAP (0.0–0.3% with respect to the blast furnace slag weight) and different extra water additions on setting time, autogenous shrinkage, compressive strength, water permeability, frost resistance, heat of hydration, and porosity is presented and discussed. The results highlight the beneficial effect of adding SAP on the mechanical and durability properties of the proposed mixtures. Only at higher percentages of SAP and additional water occur performance drops due to excessive macro-porosity of the system. It is interesting to point out that, in contrast, shrinkage always decreases as the percentages of SAP addition and additional water increase, although it cannot be completely eliminated. Experimental evidence also highlights that significant benefits can be gained from using this material in harsh environments

Structural foamed concrete: preliminary studies for applications in seismic areas

The experimental research presented in this contribution highlights the possibility of producing foamed concretes with target dry densities of 1550±50 kg/m3 and 1750±50 kg/m3 for the use in structural applications, thanks to compressive strengths greater than 25 MPa. The lower structural weight compared with ordinary concrete suggests the idea of using this material in seismic areas to exploit its advantages in relation to inertial forces. However, the reduced elastic modulus compared with ordinary concrete of equal compressive strength must be considered. In addition to demonstrating the beneficial effect of reducing the maximum diameter of the fine sand used to produce the foamed concrete, this contribution also shows how the behavior of a reinforced concrete frame changes (increase in the main vibration mode and decrease of the maximum shear at the base of the frame) if the foamed concrete presented in this study is used instead of ordinary concrete of equal compressive strength

Critical assessment of CO2 emission of different concretes: foamed, lightweight aggregate, recycled and ordinary concrete

Construction materials contribute to about 75% of the CO2 emission of all the construction processes. Concrete is one of the most widely used construction materials and is thus primarily responsible for CO2 emission. In particular, 8 − 9% of global greenhouse gas (GHG) emission are produced by concrete. CO2 emissions can be considerably reduced in the construction phase through a careful selection of materials with low environmental impact or through specific admixtures. In this study, different concretes are taken into consideration, including foamed concrete, lightweight aggregate concrete, recycled concrete and ordinary concrete. A series of mix designs of these four classes of concrete, characterized by a comparable mechanical strength or a comparable density, are taken from the relevant literature and compared to one another in terms of CO2 emission. Some guidelines or possible research lines aimed at reducing CO2 emission are finally outlined in this contribution

Reuse of sheep wool fibers in the production of ultralightweight foamed concrete: effect of fiber treatment, length, and content on the mechanical properties

Concrete is one of the most widely used materials in the world. Still, its production processes, energy consumption, and high use of raw materials make it one of the most environmentally harmful materials. This study aims to enhance the sustainability of concrete by reducing the amount of binder and incorporating secondary materials into the cementitious matrix. The binder reduction is achieved by using a foaming agent that creates a microporous matrix, significantly decreasing the volume of cement in the material. Additionally, reinforcing the material with sheep wool fiber not only improves its mechanical properties but also gives a new purpose to a commonly discarded secondary material. The research specifically seeks to identify the most effective treatments for sheep wool fiber (including non-treated, salt-treated, lime-treated, NaOH-treated, and surfactant-treated fibers), as well as the optimal fiber length (6, 12, and 20 mm) and content (4.5, 9, and 15 kg/m³) for ultralightweight foamed concrete in terms of mechanical strength. The findings demonstrate excellent compatibility between wool fibers and ultralightweight foamed concrete, with fiber-reinforced samples showing up to a 60% increase in flexural strength and up to a 50% increase in compressive strength. Among the various fiber treatments evaluated, surfactant-treated fibers yielded the best results

Fiber-reinforced lightweight foamed concrete panels suitable for 3D printing applications

This contribution presents a set of experimental results on fiber-reinforced innovative lightweight panels (FRIL-panels) having thickness of 12mm. These panels are prepared with a peculiar foamed concrete that has a high viscosity and cohesion in the fresh state, which makes it particularly suitable for 3D printing applications. The FRIL-panels can be used for internal partitions, external infills, and suspended ceilings of buildings as more effective solutions than conventional plasterboard ones, with better thermal insulation and acoustic absorption properties due to the internal air-void microstructure. The aim of this work is to investigate the out-of-plane resistance of FRIL-panels, prepared with a density of 800kg/m3, under displacement-controlled three-point bending tests. In view of potential use in the precast industry, the FRIL-panels were placed into an accelerated concrete curing tank so as to speed up the overall production process. Modulus of rupture, ultimate deflection and collapse mode of FRIL-panels are critically analysed and discussed

Enhancing Cement Paste Properties with Biochar: Mechanical and Rheological Insights

Biochar, the solid sub-product of biomass pyrolysis, is widely considered an effective water retention material thanks to its porous microstructure and high specific surface area. This study investigates the possibility of improving both mechanical and rheological properties of cement pastes on a micro-scale. The results show that using biochar as a reinforcement at low percentages (1% to 5% by weight of cement) results in an increase in compressive strength of 13% and the flexural strength of 30%. A high fracture energy was demonstrated by the tortuous crack path of the sample at an early age of curing. A preliminary study on the rheological properties has indicated that the yield stress value is in line with that of self-compacting concrete