Lightweight Concrete
In place of conventional aggregates, lightweight coarse and occasionally lightweight fine particles are used to create lightweight concrete, a specialized combination. Compared to conventional weight concrete, which has an in-place density (unit weight) of 140 to 150 lb/ft³ (2240 to 2400 kg/m³), this type of concrete typically has an in-place density (unit weight) ranging from 90 to 115 lb/ft³ (1440 to 1840 kg/m³). Lightweight concrete must have a compressive strength of at least 2500 psi (17.0 MPa) for use in structural applications. Typically, expanded shale, clay, or slate are the lightweight aggregates used in structural lightweight concrete. These materials are fired in a rotating kiln to create a porous structure. Products like as slag from air-cooled blast furnaces are also used.
distinct aggregate materials can be used to create distinct classes of non-structural lightweight concrete (LWC) with lower densities and more air voids in the cement paste matrix, as demonstrated by cellular concrete.
Types of Lightweight Concrete
Based on how they are made, different kinds of lightweight concrete can be categorized as follows:
1. Lightweight Aggregate Concrete: Concrete made using porous lightweight aggregates that have a low apparent specific gravity—typically less than 2.6—is known as lightweight aggregate concrete.
2. Aerated Concrete: Large gaps are incorporated into the concrete or mortar mass by aerating it using stabilized foam or by entraining air into the concrete.
3. Concrete with no fines: removes fine aggregate from the mixture, leaving a lot of interstitial voids. For this form of concrete, coarse aggregate of normal weight is typically utilised.
Additionally, lightweight concrete can be categorised based on its intended application, with ASTM C 330-82a for structural lightweight concrete, ASTM C 331-81 for concrete used in masonry units, and ASTM C 332-83 for insulating concrete being the three different categories. According to ASTM guidelines, structural lightweight concrete is categorised based on a minimum strength requirement
Different Types of Lightweight Concrete based on minimum strength
1. Lightweight Aggregate Concrete:
The UK began to adopt the use of lightweight concrete blocks for the load-bearing inner leaf of cavity walls in the early 1950s. The introduction of lightweight concrete (LWC) appropriate for structural work was made possible by new varieties of artificial lightweight aggregates (LWA). The following are some examples of lightweight aggregates that work well with structurally reinforced concrete:
(i). Pumice: In Germany, used mostly for industrial roofs, for reinforced concrete roof slabs.
(ii). Famed Slag: The first lightweight aggregate made in substantial quantities in the UK that is appropriate for use with reinforced concrete.
(iii). Expanded Clays and Shales: Known by several commercial names, these materials are capable of reaching a high enough strength for prestressed concrete.
2. Aerated Concrete:
Aerated concrete is strong, has the lowest density, and may be fastened with nails, screws, and saws much like regular wood. It is often offered as precast units for floors, walls, and roofs and is steam-cured under high pressure.
3. Concrete with no fines:
made entirely of coarse aggregate and cement, with voids evenly spaced throughout the bulk. Applications for it include interior wall casting, non-load-bearing walls, load-bearing walls, and underfloor filling.
Types of Lightweight Concrete Based on Density & Strength
(i). Low density concrete: It has a high thermal insulation value, a low unit weight, and a relatively low compressive strength; it is mostly used for insulation.
(ii). moderate density concrete: In between low density and structural concrete, moderate density concrete provides a good mix of strength and insulation.
(iii). structural concrete: Aggregates used in structural concrete must meet minimal requirements for compressive strength while still being appropriate for structural efficiency.
The majority of structural LWC can produce concrete that has a compressive strength more than 34.47 N/mm³. Structural LWC has a significantly higher unit weight than low-density concrete, but its thermal insulation values are significantly higher than those of regular weight concrete.
The Benefits and Uses of Lightweight Concrete
There are several uses for lightweight concrete, such as screeds, walls, insulation, and structural components. Its benefits include decreased dead load, quicker building rates, less expensive transportation, and improved thermal insulation qualities, all of which help to make buildings more energy-efficient
The Durability of Lightweight Concrete
The ability of a substance to tolerate the influence of its surroundings is known as durability. The long-term performance of lightweight concrete in a variety of environmental circumstances necessitates the implementation of appropriate precautions and preventative measures in response to problems including chemical attack, physical stress, and mechanical damage.