LATERIZED CONCRETE - CONSTITUENTS, EFFECT OF HEAT, & ITS RESIDUAL STRENGTH

LATERIZED CONCRETE (LATCON)

Laterized concrete can be defined as concrete in which stable laterite fine replace aggregate (i.e., Sand). Adepegba(1975) was recognized as the first to study the effect of using laterite as fine aggregate in concrete while he was recommended laterite up to 40% in clay for laterized concrete”.

In is further research, Adepegbe (1975) was also compared resistance to high temperature, modulus of elasticity and compressive and tensile strength of laterized concrete mixes (1:2:4; 1:1.5:3 and 1:1:2 by weight) with that of normal concrete.

He accomplished that for high strength and workability only 25% of sand in concrete should be substituted with lateritic fine, while the mix ratio should be 1:1.5:3 (cement: sand/laterite: granite) with a water/cement ratio of 0.65 and it could also be a concrete in which the fine aggregates (sand) are lateritic soils.”

Laterite as a mixture of clayey iron and aluminum oxides and hydroxides formed as a result of the weathering of basalt under humid, can be fully or partially replacement of sand in LATCON. Also from the study effect of varying sand content of laterized concrete by Balogun and Adepegba [1982] stated that the most suitable mix of laterized concrete for structural purpose is 1:1.5:3 using batching by weight with a water/cement ratio of 0.65, provided that the laterite content is kept below 50% of the total aggregate content. Which can be good for structural member? That is, containing laterite as a full or partial replacement for sand.”

CONSTITUENTS OF LATERIZED CONCRETE

Mallet (1883) was perhaps the first to introduce the chemical concept for establishing the ferruginous and aluminium nature of lateritic soils. Fermor (1911) from his study, defined various forms of lateritic soils on the basis of the relative contents of the so-called lateritic constituents (Iron, Aluminium, Titanium and Manganese in relation to silica.

Also Lacroix (1913) divided laterite into:-true laterite, silicate laterite, and lateritic clays depending on the relative contents of the hydroxides. However, there are other several attempts by the researchers to classify laterite in terms of their chemical compositions, but Fox (1936) has verified that such classifications are inadequate, other than in relations to deposits that may be exploited for their minerals content, classification based on chemical composition cannot be used to distinguish between indurate and softer formations.

The combine silica content is low in sesquioxides. This combined silica is predominantly in the form of Kaolinite, the characteristic clay mineral of most tropical formation. It was on this basis that D’hoore (1954) made a theoretical calculation of free Al2O3 content from combined silica content employing the formula:

Free Al2O3 = Total Al2O3 — (SiO2 x 0.849), The use of this procedure leads to the statement that alumina was present mainly in combined form in laterite of Buchanan’s type. Although alumina is the main constituent, the sesquioxides of iron are most common and the most frequent.””

EFFECT OF HEAT ON LATERIZED CONCRETE

Laterised concrete is one in which the fine aggregate has been partially or wholly substituted with laterite soil in its natural form its neglect as a structural engineering material is connected with the unlikelihood of its strength of the structural.

Ikponmwosa and Salau (2010) from their study, the effect of heat on laterized concrete. While the Cube specimens were cast, cured and subjected to elevated temperatures of 250oc, 500oc and 750oC.

The content of laterite in the fine aggregate was varied from 0 – 100% at 25 interval. Specimens cured at 7 and 28 days were subjected to uniaxial compressive loading tests at room and elevated temperatures. The outcome of their tests results showed that normal concrete cannot withstand large load above 250oC while laterized concrete with 25% laterite in the fine aggregate is able to resist higher load with increase in strength at higher temperatures. The peak compressive strength value of 30.44N/mm2 is recorded for the mix with 25% laterite – 75% sand at 500oC.And also when it is exposure to high temperatures causes the modulus of elasticity to decrease in all specimens irrespective of the preload condition and the strength of concrete. Also Oluwaseyi and Mnse (2007).

Described the weathering characteristics of laterized concrete with laterite-granite fines ratio as a factor in ascertaining its suitability as a substitute for the conventional fine aggregate, They found that the compressive strength of laterised concrete with laterite-granite fines decreased when subjected to alternate wetting and drying. It was also observed that laterised concrete with 40-60% laterite-granite fines subjected to a temperature variation range of 75-125oC attained compressive strength of 22.52 N/mm2. However, the critical failure temperature of the laterised concrete is yet to be ascertained.”

RESIDUAL STRENGTH OF LATERIZED CONCRETE

“A structural component exposed to devastating fires accidentally for long periods (exceeding fire resistance duration) resulting in high rise of temperature and decrease strength, while the reduce in strength of the component is called the residual strength (Kumar, 2003).

The data on the residual strength of laterized concrete desires to be obstinate. Also, the form of changes due to high temperatures include chemical and microstructural changes, such as water migration (diffusion, drying), improved dehydration, interfacial thermal incompatibility and chemical decomposition of hardened cement paste and aggregates. These cause the changes in reduction of strength and solidness of concrete and increase irrecoverable deformation (Zhang et al, 2000).

This appearance of the conclusion of other researchers who have study that cooling concrete rapidly by fascination in water after heat pretreatment results in a thermal shock which in turn leads to lower strength values than concrete cooled freely by exposure to air after heat pretreatment (Peng et al., 2008; Yuzer et al., 2004; Chan et al., 2000).

However, from the study of residual compressive strength of laterized concrete subjected to elevated temperature by F.Udoeyo(2010). He was concluded that the compressive strength of LATCON decreased in a similar manner to that of plain concrete when subjected to elevated temperatures between 200 and 600ºC. Deterioration in strength for both types of concrete was severe at 600ºC. And the plain concrete experience a better proportion of its relative residual strength than LATCON. The results indicate that the cooling regime also significantly influenced the residual compressive strength of LATCON.”