A Review on Expansive Soils Stabilized with Different Pozzolanic Materials

Soils that cause effective damages to engineer structures (such as pavement and foundation) are called problematic or difficult soils (include collapsible soil, expansive soil, etc.). These damages occur due to poor or unfavorited engineering properties, such as low shear strength, high compressibility, high volume changes, etc. In the case of expansive soil, the problem of the shrink-swell phenomenon, when the soil reacts with water, is more pronounced. To overcome such problems, soils can be treated or stabilized with many stabilization ways (mechanical, chemical, etc.). Such ways can amend the unfavorited soil properties. In this review, the pozzolanic materials have been selected to be presented and discussed as chemical stabilizers. The selected pozzolanic materials are traditional, industrial, or byproducts, ashes of agricultural wastes, and calcined-clay types. They are lime, cement, blast furnace slag, fly ash, silica fume, rice husk ash, sugarcane straw ash, egg ash, coconut husk ash, and metakaolin. In general, the stabilization of expansive soils with pozzolanic materials has an essential impact on swelling and Atterberg-limits and positively affects compaction and strength parameters. However, there is a wide range for the percentages of pozzolanic materials used as stabilizers. The content (15% to 20%) is the most ratios of the stabilizers used as an optimal percentage, and beyond this ratio, the addition of the pozzolanic materials produces an undesirable effect.

Performance of sustainable self-compacting fiber reinforced concrete with substitution of marble waste (MW) and coconut fibers (CFs)

Self compacting concrete (SCC) is special type of concrete which is highly flowable and non-segregated and by its own mass, spreads into the formwork without any external vibrators, even in the presence of thick reinforcement. But SSC is also brittle nature like conventional concrete, which results in abrupt failure without giving any deformation (warning), which is undesirable for any structural member. Thus, self-compacting concrete (SCC) needs some of tensile reinforcement to enhance tensile strength and prevent the unsuitable abrupt failure. But fiber increased tensile strength of concrete more effectively than compressive strength. Hence, it is essential to add pozzolanic materials into fiber reinforced concrete to achieve high strength, durable and ductile concrete. This study is conducted to assess the performance of SCC with substitutions of marble waste (MW) and coconut fiber (CFs) into SCC. MW utilized as cementitious (pozzolanic) materials in percentage of 5.0 to 30% in increment of 5.0% by weight of binder and concrete is reinforced with CFs in proportion of 0.5 to 3.0% in increment of 0.5% by weight of binder. Rheological characteristics were measured through its filling and passing ability by using Slump flow, Slump T50, L-Box, and V-funnel tests while mechanical characteristics were measured through compressive strength, split tensile strength, flexure strength and bond strength (pull out) tests. Experimental investigation show that MW and CFs decrease the passing ability and filling ability of SCC. Additionally, Experimental investigation show that MW up to 20% and CFs addition 2.0% by weight of binder tend to increase the mechanical performance of SCC. Furthermore, statistical analysis (RSM) was used to optimize the combined dose of MW and CFs into SCC to obtain high strength self-compacting concrete.

Optimization of bentonite modified cement mortar parameters at elevated temperatures using RSM

The inaccessibility of industrial wastes necessitated the search for natural pozzolanic materials. This paper deals the optimization of bentonite utilization in cement mortar at elevated temperatures using response surface methodology. The substitution of calcined bentonite (0%, 10%, 20% and 30%) and temperature exposure (24°C, 200°C, 400°C and 600°C) were taken as variables. The compression strength and strength activity tests for all mixes were carried out for bentonite. Design Expert 11.0 version was utilized for modelling using RSM. The peak compressive strength was displayed by 20% replaced bentonite calcined at 200°C cement mortar after 28 days curing. Strength activity was improved upon increasing the percentage of bentonite calcined at 200°C. The generated models from RSM are significance in all the factors considered. Optimum solutions were proposed with more than 0.90 desirability.

How Efficient are LC3 and GGBFS-Contained Mortar Mixtures Submerged into Na2SO4 Solution against External Sulfate Attack at an early Age?

Ordinary Portland cement (OPC) is one of the most widely used construction materials in civil engineering infrastructure construction but it is susceptible to sulfate attack. One of the ways to improve the sulfate resistance of an OPC mortar/concrete is to replace a certain amount of OPC with different pozzolanic materials such as ground granulated blast furnace slag (GGBFS) and metakaolin. The use of pozzolanic materials to mortar/concrete not only enhances durability but also reduces carbon dioxide (CO2) emission due to the less usage of OPC at the initial construction state. As considering these aspects, limestone calcined clay cement (LC3) has been developed in recent decades. However, the influence of LC3 on sulfate attack resistance has not been fully evaluated. Therefore, this study investigated the efficiency of LC3 mortar mixtures against sulfate attack at an early age (approximately 4.5 months) after two different curing periods, namely 1-day and 3-day curing, since the strength of the LC3 mixture is lower than OPC mixtures. To evaluate the synergistic effect of a combination of LC3 and GGBFS on the sulfate resistance, the LC3 and OPC mixtures containing 25% GGBFS were also assessed in terms of density, porosity, compressive strength, volumetric expansion, and weight changes. The experiment results show that the expansion of the LC3 mixture regardless of the addition of GGBFS and an initial curing strength made a plateau after a rapid increase up to 7 days, while the expansion of the OPC mixture kept increasing throughout the period. Furthermore, the addition of GGBFS to OPC or LC3 mixture provides the synergistic effect on reducing the expansion due to sulfate attack. Therefore, if LC3 mixture has high initial strength (min. 15 MPa) and dense microstructure to minimize the penetration of sulfate ion into the mixture, it is expected that LC3 mixture is more efficient than OPC mixture against the sulfate attack.

EFFECT OF ADDING WOOD POWDER ASH ON CBR VALUE IN STABILIZED HIGH PLASTICITY CLAY CEMENT AND LIME

<p>Cement and lime are widely used as stabilizing agents for soft clays. Some pozzolanic materials have also been used as additives such as asphalt, geosta, fly ash (geopolymer), base ash, salt. Industrial waste such as rice husk ash, coal burning ash (geopolymer) is also used as an alternative for stabilization materials. This research aims to study the effect of sawdust ash, as wood waste, to replace cement and lime on the stabilization of high plasticity clay. The effectiveness of sawdust ash, in this study, was evaluated from the CBR value. The test samples were also reviewed under conditions with and without immersion and with and without curing. Based on the test results, lime is very effective as an additive because it increases the CBR value of more than 100 at a level of 10%. Wood husk ash also increases the CBR value by 100%. The use of cement, lime and wood husk ash requires curing time so that there is a strong bond between the clay and additives. The use of additives without curing did not increase the CBR value. In the stabilization of clay with 10% lime, replacement of lime with wood husk ash by 4%-6%, can be used as a road sub-grade with good quality.</p>

Flexural strength of silica fume, fly ash, and metakaolin of hardened cement paste after exposure to elevated temperatures

The mechanical properties of concrete based mainly on flexural and compressive bearing capacity. Generally, researchers have an interest in the evaluation of compression property through the importance of the flexural performance of the material in the constructions, namely the significance of each mechanical property based upon the position of the structural element. The present experimentally work is directed toward improving the flexural strengths performance of ordinary hardened cement paste (HCP) at ambient and after elevated temperatures exposure. The used parameters were different pozzolanic materials with different replacements ratios to cement mass and different levels of temperature. Results proved the significant contribution of pozzolanic material to enhance the flexural properties of HCP after being exposed to elevated temperatures. The low content of CaO, the high grinding fineness, and the physical morphology of the used pozzolanic materials, made their adoption effective to HCP after exposure to elevated temperatures. Using 3%, 12%, and 15% of silica fume (SF), metakaolin (MK), and fly ash (FA), respectively, showed the highest heat endurance among the other replacements. However, the optimum replacement of MK has shown a better heat endurance than the optimum replacements of SF and FA. On the other hand, the spalling has occurred at high replacements of SF. Finally, the results are supported by means of thermo-gravimetric, SEM, and computed tomography investigations.