Literature Review
The term lightweight concrete (LWC) is used to refer to low density course aggregates such as shale, slate and clay. It is these materials that make the concrete light in weight due to the low density ability in them. Studies show that structural lightweight concrete (SLWC) usually has an in-place density that ranges from 90 to 115 lb/ft³ which is different from the regular or rather normal weight concrete (NWC) that have an in-place density that ranges from 140 to 150 lb/ft³ (Lo et al. 2009). For a long time, there have be many studies and experiments that have been conducted to reduce the weight in concrete without affecting properties considering the fact that concrete is often used as heavy building material. It is in the 1920s and the 1930s that numerous varied kinds of lightweight concrete were developed (Carneiro et al. 2019). Some of the LWC that were created during this time comprise of Argex, Durisol and Siporex among others. The low density characteristic makes LWC an ideal material particularly for building modern day structures that often call for minimal cross sections in their foundation. Moreover, SLWC are considered are considered effective since they have higher compressive strength of around 7000 to 10,000 psi. Challenges usually arise since they at times compromise the density of the mixture since they need additional water to decrease the additional mixtures of the concrete. Therefore, many studies are being currently carried out to find ways of reducing the amount of water incorporated to reduce the additional mixtures in the concrete. From the studies that have been conducted around concrete and its features, it has been ascertained that the major difference between normal and lightweight concrete is their composition. Akhnoukh (2018) notes that concrete components are a mixture of Portland cement, water and mineral aggregates. However, there are other components that might be added to attain certain desired characteristics. Some of these units are the likes of pigments, air entraining agents, waterproofing agents and pigments. Certain kinds of lightweight aggregates are what makes different types of lightweight concretes. This literature review explores different factors surrounding lightweight structural concrete by focusing on the strength that is imposed by expanded shale, clay and slate (Lo et al. 2009). The literature review will examine some of the LWC characteristics that makes it more effective compared to normal weight concrete in modern building and construction industry. Some of the differences between the NWC and LWC will also be explored to ascertain the strength effectiveness of LWC particularly the ones that use expanded clay, shale and slate (Lo et al. 2009).
Huda et al (2016) conducted a study to examine new innovation that can be used in place of regular concrete. Their argument is that there is a recent trend of globalization that has led to massive construction which in turn has brought about radical destruction of natural stone deposits. However, in order to meet the high demand of the typical weight aggregate during the production of concrete which is very important for ecological imbalances, there is need of using environment friendly alternatives. There is sufficient literature showing that management of solid waste from manufacture and agricultural industries is a major challenge that remains unsolved. According to the researchers, the use of structural lightweight concrete is an innovative remedy that will aid in the reduction of the negative effect that concrete manufacturing has on the environment (Carneiro et al. 2019).
When dealing with concrete, the strength of the materials is a crucial factor. Hossain (2019) explores the behavior of different kinds of concrete. The concrete types that have been examined comprise of normal concrete, lightweight concrete, crumb rubber concrete, ultrahigh strength concrete, self-consolidating concrete and engineered cementitious composite. In his study, he notes that there is sufficient literature which notes that strength enhancement and enhanced ductility of concrete filled steel tube columns (Zhuang, Chen & Ji 2013).
Differences in carbonation among similar LWA concrete materials comes from different facets such as the density, moisture and strength of the concrete. Also, water and cement ration play a critical role in influencing carbonation. Another factor that affects carbonation ratio is aggregate and cement ratio. Research shows that carbonation is abridged by increasing the density and moisture. Also, reducing water to concrete and aggregate to concrete ration reduces carbonation (Carneiro et al. 2019).
Carneiro et al (2019) examined the elastic components of lightweight expanded clay. According to the researchers, inverse engineering is an effective mechanism when employed in defining the elastic constants of the spherical porous solids. They identify Lightweight Expanded Clay (LECA) as aggregate particles that are processed through high temperature gas infiltration and expansion of the solid clay that is employed in filling concrete and aluminum composites. The researchers claim that despite the fact that the properties of the stated composites have been widely and thoroughly studied, there are still limited studies on the components of LECA itself. Particle diameter has a critical role because of the differing ration between the external skin thickness and porous internal structure (Carneiro et al. 2019).
Lo et al (2009) examined the impact that high temperatures have on the carbonation and strength of pozzolanic SLWC. In their study, they note that, statistically, there is a good correlation between the compressive strength of concrete and carbonation. Moreover, the compressive strength is inversely proportional to carbonation. On the other hand, carbonation performance can be improved by an extensive initial curing duration of PFA incorporated concrete. The reason behind this finding is because of better pore refinement that is attained in the course of enhanced initial moist curing. The findings from Lo et al (2009) study showed that accelerated curing at 60 degrees Celsius for three days enhanced the 28 day comprehensive strength of the pulverized fuel ash and silica fume incorporated mixes. However, in led to higher carbonation of the mixes in comparison to when curing is done at normal temperatures (Lo et al. 2009).
Costa, Carmo and Júlio (2018) examined the influence that LWAC has on the bond strength of concrete to concrete interfaces. The experimental research was conducted to distinguish between the strength of LWAC bond and normal density concrete (NDC). The findings of the study revealed that the function of the binding matrix strength and of the kind of the aggregate while in the interface strength, it relies on the roughness of the substrate. The resultant coefficients of the friction cohesion showcased a good correlation with the roughness of the parameter. Their study showed that cohesion was significantly influenced by the matrix strength of the additional concrete. A conclusion drawn from Costa, Carmo and Júlio (2018) study is that when tending to increase the roughness of a surface above a particular limit, there is no benefit in relation to tensile and shear strengths of the interfaces with lightweight aggregates concrete.
LWC that incorporates a porous aggregate might have a carbonation feature that is different from NWC. According to Lo et al (2009), carbonation of LWC is influenced by both the chemical and physical components and the kind of the LWA. There is literature that suggests that LWC with pumice and polystyrene aggregate showcased higher levels of carbonation compared to NWC due to the high suction of water and carbon dioxide by polystyrene and pumice (Carneiro et al. 2019). On the other hand, LWCs that is created with natural or even artificial LWA are instrumental in decreasing structure deadweight. There are studies which have examined the strength of lightweight volcanic pumice concrete particularly in steel hollow parts in comparison to normal concrete, findings suggest that there strength are almost equal. Nevertheless, Hossain (2019) suggests that there is need of more studies to assess the behavior of lightweight concretes with different LWAs. For example, the behavior of LWC with LWAs such as expanded shale and clay ought to be examined further. From the many studies that have been explored, it is apparent that there is limited literature exploring the integration of expanded shale, clay and slate (Zhuang, Chen & Ji 2013).
Carneiro et al. (2019) note that concrete is combination of aggregates, cement, water and other additives. The term lightweight is added to all the varied kinds of concrete that have low density compared to normal weight concrete. Reducing the weight of concrete is usually attained through the use of lightweight aggregate in concrete, the use of foamed concrete and the use of autoclaved aerated concrete. However, there are other mechanisms that are not used very often to reduce the weight of concrete. While normal weight concrete weighs around 2240 to 2450 kg/m3, lightweight concrete weighs around 300–2000 kg/m3. However, the practical range of density for lightweight concrete is around 500-1850 kg/m3 (Lo et al. 2009).
There are different kinds of LWA that can be employed in the production of LWAC. Some of the examples comprise of volcanic pumice and thermal treated natural raw materials. Examples of thermal treated natural raw materials are expanded clay, shale and slate among others. A good example of expanded clay is lightweight expanded clay aggregate (LECA) (Lo et al. 2009). It is a multipurpose material that is employed in increasing the number of applications especially within the construction industry. Within the construction industry, LECA is employed in the creation of lightweight concrete, structural elements and blocks among others. On the other hand, an example of expanded glass is poraver. The final product that is attained in lightweight concrete is usually as a result of the type of lightweight aggregate that was used (Zhuang, Chen & Ji 2013). Formed concrete (FC) on the other hand is created by adding a considerable amount of entrained air commonly around 20% to 50% in concrete. Some of the characteristics that FC have is low density, self-compacting, pumpable and self levelling. Usually, it is employed as a nonstructural concrete that is often used for filling voids in construction infrastructure. This study focuses on concretes particularly the LWAC which is considered under the American Concrete Institute as suitable for structural applications. For a concrete to be categorized under structural lightweight concrete, Zhuang, Chen & Ji (2013) assert that it should have a minimum of 28 days compressive strength and a maximum density of around 17 MPa and 1840 kg/m3. The practical variation for density in SLWC is around 1400 kg/m3 to 1840 kg/m3. Concrete is considered to be nonstructural when they are made of lower densities but with higher air voids in the cement paste
Lopez, Kahn and Kurtis (2010) asserts that rotary kiln lightweight aggregates (LWA) have been employed in the making of varied kinds of lightweight concrete. Naturally, LWAs are found in random particle shapes due to volcanic emissions. On the other hand, expanded shale, clay and slate are manufactured via the rotary kiln where the the raw lightweight volcanic emissions are heated at a temperature that is above 1000 degrees Celsius. The aggregate that is produced is categorized basing on the quality, lightweight, strength, absorption capacity and durability.
Qadir, Adnan, and Gazder (2017) states that that there are minimal studies that have been conducted regarding the use of effectiveness of LWACF. For this reason, many developing countries are still struggling to use it within the building and construction industry. However, building and construction industries in developing countries have found LWACF to be very effective. The findings from the study showed that the beams that were fabricated with LWACF had good resistance to crack in comparison to the ones fabricated using normal weight concrete. Their study also revealed that LWACF is a very efficient material for construction of water tanks due to its structure and ability to sustain heat. Recently, new generation of HPCs have been created by including varied materials with superior fresh conditions and durability components compared to normal concrete. Some of the incorporated materials by the new generation HPCs are fibers, LWAs, supplementary cementing materials and industrial wastes.
Huda’s et al (2016) study proposes the use of reinforced oil palm shell and palm oil clinker concrete (PSCC) beam. The SLWC, PSCC is made by combining oil palm shell and palm oil clinker. These raw materials are preferred since they are agricultural wastes which have been proven to be effective in the production of concrete. The findings from the study showcase that PSCC beams have typical flexural performance and experiences ductile failure providing enough warning prior to failure. However, for the beams that had higher reinforcement ratio, the deflections at the service loads surpassed the limit indicating the need to increase the depths of the beams.
Li et al (2019) study revealed that steel fibers have the potential of strengthening SFRELC beams in terms of shear performance even when web reinforcement is not present. In examining LWAC’s tensile strength, Bogas, Alexandre, and Nogueira (2014) found out that the material was stronger compared to the normal weight aggregate. Also, it had less porous aggregates and less tensile structural efficiency compared to the conventional concrete.
Lopez, Kahn and Kurtis (2010) conducted an experiment to evaluate the mechanical properties and shrinking behavior of low water to cementious materials of lightweight aggregate. The findings revealed that shrinking capacity of the materials were high in the past and not in the aggregate for both high performance concretes and normal concrete. Also, the use of pre wetted LWA improved the hydration and development strength within the first 12 months.
Malešev et al (2014) on the other hand, examined the impact of LWA on the kind and volume of cement. Their study found out that the kind of cement does not have a major effect on the investigated. However, the amount of cement has to be considered. In another study conducted by Kim et al (2017), the researchers examined the design and use of structural lightweight concrete for floating concrete structures within marine environments. From their study, findings indicate that concrete strength and density are some of the crucial factors that should be taken into consideration by structural designers and structural engineers who have an interest in using SLWC for floating concrete structures. Literature from the study shows that previous studies concluded that abridged concrete density, usually lower than 1,800 kg/m3 significantly led to better stability when applied to floating oil storage tanks that were subjected to wind and other loads.
In conclusion, the literature review has clearly shown that LWC is a very effective type of concrete in the modern day building and construction industry. Expanded clay, shale and slate are the main materials that are used for the production of lightweight concrete that have been found to exhibit the highest strength. Despite the availability of the used literature, the exploration conducted has depicted that there are limited structures that have explored the strength of structural lightweight concrete. Therefore, there is dire need for more studies to be conducted on the subject for effective LWC materials to be developed that will reduce density without the need for more water which plays a key role in reducing the density during use. However, LWC has been confirmed as an effective concrete material for the building and construction industry. SLWC has also been associated with efficiency since it plays a key role in conservation of the environment unlike other kinds of concrete inclusive of NWC.
References
Akhnoukh, A. K. (2018). Internal curing of concrete using lightweight aggregates. Particulate Science and Technology, 36(3), 362-367.
Bogas, J. A., & Nogueira, R. (2014). Tensile strength of structural expanded clay lightweight concrete subjected to different curing conditions. KSCE Journal of Civil Engineering, 18(6), 1780-1791.
Costa, H., Carmo, R. N. F., & Júlio, E. (2018). Influence of lightweight aggregates concrete on the bond strength of concrete-to-concrete interfaces. Construction and Building Materials, 180, 519-530.
Hossain, K. M., & Chu, K. (2019). Confinement of six different concretes in CFST columns having different shapes and slenderness. International Journal of Advanced Structural Engineering, 11(2), 255-270.
Huda, M. N., Jumat, M. Z. B., & Islam, A. S. (2016). Flexural performance of reinforced oil palm shell & palm oil clinker concrete (PSCC) beam. Construction and Building Materials, 127, 18-25.
Kim, M. O., Qian, X., Lee, M. K., Park, W. S., Jeong, S. T., & Oh, N. S. (2017). Determination of structural lightweight concrete mix proportion for floating concrete structures. Journal of Korean Society of Coastal and Ocean Engineers, 29(6), 315-325.
Li, X., Li, C., Zhao, M., Yang, H., & Zhou, S. (2019). Testing and prediction of shear performance for steel fiber reinforced expanded-shale lightweight concrete beams without web reinforcements. Materials, 12(10), 1594.
Lo, T. Y., Nadeem, A., Tang, W. C. P., & Yu, P. C. (2009). The effect of high temperature curing on the strength and carbonation of pozzolanic structural lightweight concretes. Construction and Building Materials, 23(3), 1306-1310.
Lopez, M., Kahn, L. F., & Kurtis, K. E. (2010). High-strength self-curing low-shrinkage concrete for pavement applications. International Journal of Pavement Engineering, 11(5), 333-342.s
Malešev, M., Radonjanin, V., Lukić, I., & Bulatović, V. (2014). The effect of aggregate, type and quantity of cement on modulus of elasticity of lightweight aggregate concrete. Arabian Journal for Science and Engineering, 39(2), 705-711.
Qadir, A., & Gazder, U. (2017). Flexural and shear strengths of fiber modify lightweight aggregate concrete and its application in water-retaining structures. World Journal of Engineering.
Zhuang, Y. Z., Chen, C. Y., & Ji, T. (2013). Effect of shale ceramsite type on the tensile creep of lightweight aggregate concrete. Construction and Building Materials, 46, 13-18.
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