Because lightweight concrete has so many uses, it’s important to understand its durability and resistance to various climatic conditions. As a result, the following sections explore the durability of lightweight concrete. According to the American code, lightweight concrete is defined as concrete with an air-dry density of less than 1810 kg/m3. Other countries’ definitions of lightweight concrete may differ slightly. For example, according to Norway Code, concrete is considered lightweight if its saturated surface dry density is equal to or greater than 1800 Kg/m3 and its compression strength does not exceed 85 MPa. Cement, water, fine aggregate, and lightweight coarse aggregate, such as clay, slate, and expanded shale, are mixed together to make lightweight concrete.
Factors Affecting Durability
Lightweight Concrete’s Freezing and Thawing Resistance The resistance of lightweight concrete to freezing and thawing is determined by a number of factors, including aggregate types, concrete mixture proportions, aggregate moisture content, and air entrainment percentage. It has been established through tests that the durability of non-air entrained lightweight concrete is superior to non-air entrained regular weight concrete during freezing and thawing conditions, particularly when natural fines are used. This is true for the majority of lightweight aggregate, regardless of whether it has been pre-soaked or has been air dried. Under terms of air entrained performance under freezing and thawing circumstances, lightweight concrete made with lightweight aggregate performs significantly better than standard concrete in air dry conditions.
Both lightweight concrete manufactured with lightweight aggregate in pre-soaked concrete and conventional weight concrete operate similarly and with no discernible changes. High strength lightweight concrete, with compressive strengths ranging from 54 to 73 MPa, has remarkable and significant freezing and thawing resistance. Chemical Attack Resistance in a Lightweight Aggregate Because lightweight coarse particles are less prone to react with alkalis, chemical attacks may not have the same impact on lightweight concrete as they do on heavier concrete. The penetration of lightweight concrete matrix is problematic due to the high cement content and low free water to cement ratio. The majority of structural classes of lightweight aggregate concrete contain dense fines, which is why such concrete must be tested.
Abrasion Resistance of Lightweight Concrete
The strength, hardness, and toughness qualities of aggregate and cement paste, as well as the link between aggregate and cement paste, all contribute to lightweight concrete’s abrasion resistance. As the qualities of lightweight concrete improve, so does their resistance. If the aggregate particles are exposed, the lightweight aggregate’s resistance to abrasion is significantly reduced. To provide concrete surface protection through surface treatments and boost matrix quality, it is recommended to blend low density coarse aggregate and natural fine aggregate. The resistivity of lightweight concrete used in the building of bridge decks subjected to hundreds of millions of vehicle crossings has been observed to be comparable to that of normal weight concrete. Where steel-wheeled industrial vehicles are used commercially, it is recommended that certain limits be implemented.
The reaction between calcium hydroxide produced by cement hydration and carbon dioxide in the atmosphere is known as carbonation. This produces calcium carbonate, which lowers alkalinity, which protects embedded reinforcement in concrete from corrosion. The PH in concrete can predict concrete protection degradation, and it is harmful when it is dropped to roughly 9 from 13, because the reinforcement protection is lost, and steel bars are much more prone to corrosion. The majority of lightweight aggregates are porous, making lightweight concrete last longer and allowing for gas diffusion, such as carbon dioxide. This problem can be solved if a good aggregate distribution is achieved and continuous pathways through particles to the steel reinforcement are avoided in order to reduce carbonation rates.
Reinforced Lightweight Concrete Corrosion Resistance
By providing thick concrete layer and increasing the cement content, lightweight concrete’s capacity to withstand carbonation can be increased. Tests have revealed that if the cement content is greater than 350 Kg/m3, the depth of carbonation is fairly shallow. Reinforced Lightweight Concrete Corrosion Resistance Alkalinity in concrete acts as a protective layer for steel reinforcement, preventing corrosion. Concrete’s alkalinity can be raised by using a high percentage of cement, which should be larger than 350 Kg/m3 or the steel reinforcements will corrode soon. Apart from utilising a considerable amount of cement, properly compacting the concrete is quite beneficial since it contributes to the concrete’s resistance to carbonation ingression.
Lightweight concrete can be made in a variety of ways, the most common of which is by using lightweight aggregate or lightweight matrix. Natural pumice aggregate to man-made sintered aggregate like sintered fly ash are examples of lightweight aggregates that can be employed (Mindess et al., 2003). The topic of lightweight aggregate is outside the scope of this chapter and will not be covered in depth. The lightweight cement matrix filled with air, often known as aerated concrete or foam concrete, will be the centre of attention. Just & Middendorf (2009) classified distinct types of aerated concrete or foam concrete that can be made into either AAC or air cured foam concrete. As a result, there are two types of aerated concrete in general.
Types of lightweight concrete
According to Just & Middendorf, the foam can be added by mechanical or physical methods (2009). Mechanical foams are created by pounding a foaming agent together, whereas physical foams are created by introducing an already foamed solution straight into the mixing process. The latter approach, which produces uneven holes, has been found to produce more regular and stable pores than the former (Just & Middendorf, 2009). Normally, this foam concrete is air cured. AAC is a type of lightweight concrete that is formed by inflating new concrete with gas bubbles and then curing it in a high-pressure steam curing system known as autoclaved. In the manufacturing of AAC masonry blocks, the autoclaved aerated process is commonly utilised. This is it.
Comparing the density of the particle to that of typical natural aggregate, such as a reference particle density of 2.6 Mg/m3, is the most acceptable technique of determining particle density in structural concrete. Most aggregates have densities close to 2.6 Mg/m3 in their solid structure, whether lightweight or not, but it is the air within the structure of an aggregate that allows compacted structural concrete to be less than 2000 kg/m3. It’s critical to comprehend the distinction between the two definitions of density. The mass per unit volume of individual aggregate particles, as measured by BS EN 1097-33, is referred to as particle density. The mass of dry particles enclosed inside a certain volume as determined by dry loose bulk density.
Lightweight aggregate concrete
Lightweight aggregate concrete is constructed with natural or artificial lightweight aggregates such as gravel or crushed stone. As a result, it has a lower bulk density than concrete. Furthermore, because a variety of aggregates can be utilised, concretes of various densities and strengths can be designed. Low-density concretes, structural lightweight concretes, and moderate-strength lightweight concretes are all examples. The next sections go over each of these points. Low-density concretes and their aggregates Because of their high thermal insulation characteristics, low-density concretes are commonly utilised for insulation. They have a density of less than 800 kg/m3. They have a low compressive strength of 0.7 to 7.0 MPa due to their low density. Aggregates such as vermiculite and perlite are widely used. Bulk density has been estimated to be in the region of.
Following are the factors that affect the durability of concrete, Cement Content, Aggregate Quality, Water Quality, Concrete Compaction.
Concrete strength is affected by many factors, such as quality of raw materials, water/cement ratio.
However, excess water in the concrete could increase the gap between aggregates.