Porous Lightweight Aggregate Research Articles

Advanced moisture control in porous aggregates for improved lightweight high-performance concrete

The porous lightweight aggregates in concrete experience a process of water absorption and desorption. This study aims to improve the performance of water-sensitive low water/binder (w/b) systems by effectively utilizing these water regulations. The effects of expanded shale (ES) substitutions and saturation levels (dry, half saturation, and saturation) on the fresh and hardened properties of mixtures with a w/b of 0.18 were investigated. The results indicated that, during the fresh stage, water absorption reduced workability and shortened the setting time. In the hardening stage, the released water improved hydration, increased internal relative humidity, and caused volumetric expansion, which reduced autogenous shrinkage. A comprehensive evaluation revealed that the optimal condition for ES was half-saturation with 4.0 wt% pre-absorbed water. This condition achieved the best internal curing effect, improved workability, and optimal structural efficiency (strength/density). This study provides practical insights for the effective integration of porous aggregates in the mixture design and engineering applications.

Understanding and predicting micro-characteristics of ultra-high performance concrete (UHPC) with green porous lightweight aggregates: Insights from machine learning techniques

Ultra-high performance concrete (UHPC) is an advanced material in construction. Porous lightweight aggregates (PLWA) could reduce the self-shrinkage risk of UHPC by maintaining internal relative humidity. However, understanding and predicting the water migration processes influenced by PLWA are still challenging. Given that machine learning (ML) has shown promise in modeling complex relationships, this study aims to create a reliable ML model to predict and analyze the micro-properties of UHPC with different green PLWAs (pumice and phosphogypsum aggregates). Furthermore, it aims to enhance our understanding of how PLWA influences the microstructure development within the UHPC. The research results demonstrated that convolutional neural network (CNN) algorithm with an R2 value exceeding 0.95 in both the test and training data. Meanwhile, the CNN was employed to predict time-dependent water content and hydration degree of UHPC containing various types of PLWA and multiple-aggregates, aiding in the exploration of how different PLWA impact the water migration of UHPC. Based on the ML analysis results, pumice aggregates and multiple-aggregates both contributed to reducing the rate of water migration, subsequently reducing UHPC shrinkage. Finally, some insights on the use of ML techniques for predicting and understanding the micro properties of UHPC were discussed. ML was employed for micro-performance prediction and in-depth analysis, thereby advancing the intelligent evolution of green UHPC products.

Micromechanical and chemical characteristics of interfacial transition zone in alkali-activated slag concrete containing lightweight iron-rich aggregates

This study explored the time-varying alkali-activation effects of the lightweight aggregates (LWA) on the interfacial transition zone (ITZ) of the alkali-activated slag concrete with different curing ages, molar ratios, and alkali concentrations from 28 to 300 d. The improved micromechanical performance of the ITZ at 28 d stemmed from the early-age internal curing effect of the porous LWA. However, the post-28 d internal curing effect diminished, with the alkali-activation dominating the performance of the ITZ from 28 to 300 d. Although alkali-activated cement possessed early strength characteristics, the deconvolved phase results illustrated that alkali activation persisted in the ITZ between the LWA and cement from 28 to 300 d, leading to a high proportion of calcium silica aluminate hydrate. As a marker, Fe from the lightweight iron-rich aggregates mitigated into the alkali-activated cement, demonstrating the alkali-activated reaction between the LWA and alkali-activated slag matrix. Molecular dynamics simulations further characterized that the low content of Fe did not decrease the overall strength of the ITZ. The interfacial interaction energy revealed the alkali-activation between the LWA and cement compensated for the weakening of mechanical properties caused by Fe ions on the ITZ.

Energy Storage in Lightweight Aggregate and Pervious Concrete Infused with Phase Change Materials

This study explores the feasibility of utilizing pervious concrete (PC) incorporating diverse lightweight aggregates (LWAs) integrated with phase change materials (PCM) for applications where forced air cooling would be advantageous. The use of such a component provides latent and sensible heat that can cool forced air applications, offsetting ambient temperature increases that occur during the day. Macro- and microencapsulation techniques were used to incorporate inorganic PCM in the PC. The macro-encapsulation technique involved enclosure of PCM within a stable shell prior to addition into the concrete. The microencapsulation technique involved the impregnation of PCM into porous lightweight aggregate. To overcome the PCM reaction with the concrete constituents, an epoxy coating was utilized. The design of the PCM concrete mix and comprehensive laboratory assessment of porosity, water permeability, PCM absorption capacity, compressive strength, and microstructure of the LWAs are detailed. The test results indicate that LWAs have high PCM impregnation rates ranging from 32 % to 57 % by volume. The compressive strengths of PC using LWAs were reduced by 25 % to 65 % when using microencapsulation. The use of microencapsulation was found to reduce the pressure drop under air flow due to the increase in aggregate size as a result of the coating thickness. PCM-PC with a shell thickness of 100 mm, resulted in a pressure drop of less than 100 Pa at a velocity of 0.35 m/s. The use of macro-encapsulated PCM in PC was sensitive to the phase of the PCM, where the liquid phase reduced the compressive strength by 67 %. The failure occurred within the macro-encapsulated PCM at the liquid phase temperatures and at the interface between the encapsulated PCM at solid phase temperatures. The heat transfer provided by the LWA infused PCM when used in a packed aggregate bed or in PC, was shown to match expected latent and sensible heat estimates based on the thermal properties of the materials. This systematic investigation provides valuable insights into LWAs and PCM performance in pervious concrete, offering a comprehensive understanding of their interaction in cooling applications.

Effects of shape-stabilized phase change materials in cementitious composites on thermal-mechanical properties and economic benefits

• The effects of PCMs to save building energy consumption was investigated. • Physical-thermal-mechanical testing and cost analysis were conducted. • Energy saving efficiency was calculated via computational modeling. • Findings infer the potential application of coconut oil as an engineered PCM. Phase change materials (PCMs) have been utilized to improve the thermal properties of cementitious composites by using their latent heat capacity. Applying them to building components can reduce their heating and cooling loads through energy absorption during the phase change period. The shape-stabilized method using porous lightweight aggregates can prevent PCM leakage during the phase transition process. While many attempts have been made to develop and improve shape-stabilized PCM composites to achieve a high level of energy savings, their economic benefits have not been fully investigated, as most analyses are based on initial material costs with a limited linkage of their thermal-mechanical properties. This study used an integrated experimental-computational method to evaluate the effects of different PCMs in building components by considering the core thermal-mechanical properties with an economic benefit analysis. Toward that end, two different PCMs (PureTemp® and coconut oil) were selected to fabricate Thermal Energy Storage Aggregates (TESA) using the vacuum impregnated method: TESA-P (with PureTemp®) and TESA-C (with coconut oil). The thermal-mechanical properties were experimentally determined and used for building energy simulation for a typical small office in Houston, Texas. The cementitious composites incorporated with PCM showed lower thermal conductivity and heat transfer than the non-PCM specimens. The TESA-P specimens showed a more prolonged time lag and better energy-saving performance than the TESA-C specimens due to better thermal properties of PCM itself. In contrast, the costs of TESA-C applications could be less with a shorter pay-back time. The findings of this study infer the potential application of coconut oil as an engineered PCM in building construction.

3D printing lightweight aggregate concrete prepared with shell-packing-aggregate method - Printability, mechanical properties and pore structure

It is a challenge to use porous lightweight aggregates to prepare 3D printing concrete as the water absorption process of porous lightweight aggregates has significant effect on its printability, especially when the content of lightweight aggregate is relatively high. In this paper, the effects of preparation methods on the rheological properties and printability of 3D printing lightweight aggregate (3DPLWC) are studied, aiming to prepare 3DPLWC with high lightweight aggregate content. 3DPLWC with 50, 75 and 100 vol.-% substitution of fine river sand with clay ceramsite sand (CCS) are successfully prepared with shell-packing-aggregate method. The mechanical properties and pore structure of 3DPLWC with different CCS contents are then studied. It is found that the printing process has caused the anisotropy of 3DPLWC, and the specific strength of 3DPLWC is lower than cast counterparts. For 3DPLWC, the increase of pre-wetted CCS content contributes to the decrease of matrix porosity and the increase of circularities of matrix pores in the printed specimens. The results of this study can provide guidance for the preparation of 3DPLWC with different density levels.

The influence of pre-coated EGA and aerogel on the properties of lightweight self-compacting cementitious composites

Aerogel and porous lightweight aggregates have adverse impacts on the fresh, mechanical, and water absorption characteristics of concrete. In this study, styrene-butadiene rubber (SBR) and Paraffin were used to coat the lightweight aggregates. The lightweight aggregates were coated in single and double layers. Besides, aerogel particles were also coated with SBR. The properties of the cementitious composites, such as slump flow, T50 flow time, V-funnel flow time, J-ring height, compressive strength, water absorption, porosity, and microstructural analysis, were evaluated. It was observed that single-layer coatings of polymers on EGA improved the slump flow by 6.9% and lowered the water absorption by 26%. The compressive strength of the cementitious composites incorporating polymer coated EGA also improved by 15.9%. Scanning microscopy was used to evaluate the microstructure of EGA, aerogel, and lightweight cementitious composites. A uniform, denser structure of polymer coated EGA was observed in the interfacial transition zone.

Enhancing the compressive strength of thermal energy storage concrete containing a low-temperature phase change material using silica fume and multiwalled carbon nanotubes

In this study, structural functional thermal energy storage concrete (TESC) containing Tetradecane which is a low-temperature phase change material (PCM) has been developed. The PCM was incorporated in the concrete using a porous lightweight aggregate (LWA). PCM–LWAs were fabricated using vacuum impregnation technique, and a dual–layer coating having high thermal conductivity. The epoxy of high thermal conductivity was applied on the surface of PCM impregnated LWAs to prevent leakage of PCM. Differential scanning calorimetry (DSC) and thermogravimetric analysis were used to evaluate the thermal performance of encapsulated PCM–LWA. The DSC results demonstrated that PCM–LWA had melting and freezing temperature 4.18 °C and 0.33 °C and corresponding enthalpies 18 J/g and 15 J/g, respectively. Thermal energy storing concrete was developed by replacing normal-weight aggregates with the PCM–LWAs in proportions of 50% and 100% by volume. The compression test results revealed that the strength of PCM–LWA concrete decreased significantly compared to normal concrete. The strength loss in the PCM–LWA concrete with replacement ratios of 50% and 100% were 29% and 39%, respectively. Due to porous nature and relatively low stiffness of LWAs, significant strength loss has been observed. To overcome the strength degradation, silica fume (SF) and multiwalled carbon nanotubes (MWCNTs) were added to the concrete mixture. The addition of SF/MWCNTs reduced the strength loss by 15% and 20%, respectively. The SEM results revealed that the SF/MWCNT addition in concrete resulted in denser microstructure. The XRD results confirmed that SF reacted with Ca(OH)2 to increase the growth of C-S-H. Therefore, the mechanical performance of TESC containing PCM–LWAs can be improved by adding SF/MWCNTs to the concrete mixture.

Co-utilization of lake sediment and blue-green algae for porous lightweight aggregate (ceramsite) production

Lake sediment and algal sludge with large output posed significant environmental risks. In this work, an idea of co-utilization of both solid wastes for the production of ceramsite (a sort of porous lightweight aggregates as building materials) was proposed and validated for the first time. The treatment process contained a dewatering step by a flocculation-pressure filtration method, and a sintered ceramsite preparation step. Effects of flocculant type and dosage on the dewatering performance were studied in the first step. An environmental-friendly amphoteric starch flocculant with a dosage of 12 mg/(g dried sample) was found to achieve the best dewatering performance. Effects of raw material mass ratio, sintering temperature and time in the second step were investigated. Under the optimal conditions (60 wt% of dewatered sediment; 20 wt% of dewatered algal sludge; 20 wt% of additives (fly ash: calcium oxide: kaolin = 2:1:2); sintering temperature: 1100 °C; time: 35 min), the obtained ceramsite met the Chinese National Standard as a qualified building material, with reliable environmental safety according to the leaching results for both heavy metals and microcystins. Both environmental and economic benefits of the proposed treatment were assessed. The process completely followed the rules of “reduction, harmlessness and resource utilization” for solid waste treatment and disposal; Meanwhile, the profit of the proposed ceramsite production could be more than 2.3 US dollar/m3. The co-utilization method in this work acted as a good example for the comprehensive management of solid wastes in water-rich areas.

The Rapid Chloride Migration Test in Assessing the Chloride Penetration Resistance of Normal and Lightweight Concrete

Chloride-induced corrosion has been one of the main causes of reinforced concrete deterioration. One of the most used methods in assessing the chloride penetration resistance of concrete is the rapid chloride migration test (RCMT). This is an expeditious and simple method but may not be representative of the chloride transport behaviour of concrete in real environment. Other methods, like immersion (IT) and wetting–drying tests (WDT), allow for a more accurate approach to reality, but are laborious and very time-consuming. This paper aims to analyse the capacity of RCMT in assessing the chloride penetration resistance of common concrete produced with different types of aggregate (normal and lightweight) and paste composition (variable type of binder and water/binder ratio). To this end, the RCMT results were compared with those obtained from the same concretes under long-term IT and WDT. A reasonable correlation between the RCMT and diffusion tests was found, when slow-reactive supplementary materials or porous lightweight aggregates surrounded by weak pastes were not considered. A poorer correlation was found when concrete was exposed under wetting–drying conditions. Nevertheless, the RCMT was able to sort concretes in different classes of chloride penetration resistance under distinct exposure conditions, regardless of the type of aggregate and water/binder ratio.

Mitigation of thermal curling of concrete slab using phase change material: A feasibility study

In this study, the effects of phase change material (PCM) on the thermo-mechanical behaviors of concrete pavement slabs are investigated so as to test the feasibility of utilizing PCM for mitigation of thermal curling of pavement. The PCM is elaborately stabilized in porous lightweight aggregate then loaded into concrete, without compromising strength associated with PCM incorporation. Thermal analysis indicates that the PCM introduces a latent heat capacity of about 21 J/g to the pavement slab. Two emerging fiber-optic monitoring techniques, i.e., truly distributed strain/temperature sensors and a high-resolution inclinometer, are employed to continuously monitor distributions of the temperature, strain, and tilting angle of the slabs subjected to heating and cooling, respectively. Validated by the obtained experimental results, a finite element simulation framework is established to further investigate the temperature gradient distributions, slab deformations/curvatures, and thermal strain and stress inside the slabs. The results suggest that the PCM-incorporated slab has a higher top surface temperature, a larger top-vs-bottom surface temperature difference, and thereof a larger curvature. However, the temeprature gradient reveals that heat accumulates at the upper layer before PCM melts completely, thus accounting for most of the temerpature difference. Moreover, regardless of the larger top-vs-bottom strain difference and stress nonlinearity, the linear strain of the PCM slab is smaller due to its lower coefficient of thermal expansion, and the later stage stress at the middle of the PCM slab center is smaller. Based on the findings, strategies of using PCM to control thermal curling of pavement slabs are proposed.

Effect of pre‐coating lightweight aggregates on the self‐compacting concrete

AbstractThe porous lightweight aggregates adversely affect fresh properties of concrete, including slump and disruption of pumping concrete. Besides, this type of concrete is very susceptible to shrinkage cracking. In this study, two types of lightweight aggregates were used with a combination of two types of coating, including hydrophobic polymers ‐polyvinyl acetate and styrene‐butadiene rubber coatings. The coatings were applied in single and double layers. For the fresh concrete, the fresh properties of concrete, including slump flow, T50, flow time, and L‐Box were evaluated and for the hardened concrete, compressive strength, flexural strength, tensile strength, water absorption and shrinkage was studied. It was seen that the slump flow of coated lightweight aggregates increased by 10%, and also coating process reduced the water absorption of the aggregates up to 82%. The compressive strength increased by up to 21% for the coated aggregates. Scanning electron microscopy was also used to investigate the microstructure of the mortar‐aggregate interface. Microstructural images showed a uniform and dense interfacial zone of cementitious matrix‐aggregate for coated lightweight aggregates. Moreover, an improvement of 50–150 μm in the interfacial zone's thickness was seen for coated aggregates compared to uncoated aggregates.

Effect of different expanded aggregates on durability-related characteristics of lightweight aggregate concrete

Lightweight aggregate concrete (LWAC) has relatively larger porosity than conventional concrete, mainly due to the incorporation of porous lightweight aggregates. The types of used lightweight aggregates are critical in determining the physical properties of LWAC, and it is therefore important to examine their effects on the durable characteristics of the material. To perform comparative analysis, the concrete mixture designs with two theoretical density classes were developed. The mixture composition for each class was constant and the only variable parameter was the type of the used lightweight aggregates-expanded glass (Liaver®), expanded clay (Liapor®), and foam glass (Ecoglas®). Accordingly, their pore characteristics and durability-related properties, such as sorptivity, open water porosity, and water penetration depth, were examined. To understand these phenomena, the permeable characteristic, tortuosity, was also calculated using a numerical approach incorporating X-ray micro-computed tomography. The examined results confirm that the durability characteristics of LWAC are strongly affected by the used aggregate types and are highly correlated with their pore structures. In terms of permeable characteristics, expanded glass is the most beneficial material among the used particles, and the systematic approach in this study can be used to examine the durability characteristic of LWAC.

Enhancing the mechanical and thermal properties of aerated geopolymer concrete using porous lightweight aggregates

This study demonstrates the development of geopolymer foamed concrete (GFC) by introducing a double hierarchical porous structure using premade foam and lightweight porous aggregates. Hydrophobic expanded perlite (EP) was used as porous aggregate and the addition of 10% and 20% of the binder (by eliminating corresponding volumes of sand) were investigated. It was observed that the incorporation of EP has brought obvious benefits in improving the mechanical and thermal properties of GFC. The amount of foam required to achieve a similar density of GFC was reduced by 19% and 53% for 10% and 20% of EP respectively, due to the presence of the large amount of open pores in EP. The compressive strength of cube specimens has increased by 75% and 180% at 7 days and 65% and 188% at 28 days, respectively. The reaction kinetics of geopolymers studied using FT-IR reveals that the reaction rates of geopolymer binders increase with the amount of EP. It is also shown that the increase in the amount of geopolymer gel particulates surrounding bubbles is the major reason for attaining fine air voids and strong binding skeleton in GFC-20EP, compared to the other two groups. Consequently, the pore homogeneity index, as measured from the ultrasonic velocity at different directions, was improved from 50% to 90%. The thermal performance tests conducted using prototype test cells reveals that the indoor thermal conditions will significantly improve when the GFC-20EP is used as building elements. This is particularly demonstrated by the reduction in peak indoor temperature of 1.8 °C and an increase in thermal inertia of 1.7 °C with GFC-20EP, compared to GFC-s.

Effect of Aggregates with Different Physical Properties on Concrete Strength for Different Water to Cement Ratio and Different Cement Content

Aggregates have a large volume in concrete, therefore they directly affect the properties of concrete. Aggregate, which is expected to give desirable strength in concrete, should be examined especially in terms of its physical properties and grain size. In this respect, aggregate to be used in concrete must not be easily broken, non-abrasion quickly, and must be strong and hard structure. While low strength is obtained in concrete produced with porous lightweight aggregates, high strength is observed in concrete produced with high-density aggregates. In addition, aggregates have an effect on concrete properties such as concrete workability and permeability. One of the aggregates commonly used in concrete production is limestone aggregate. In this study, the effects of limestone aggregates with different properties on compressive strength and splitting tensile strength were investigated experimentally. In this context, cubic specimens of 150×150×150 mm dimensions were prepared for different water/cement ratios, different cement contents, and different aggregate properties. With these specimens, after the cure period of 28 days, the relevant strength tests were performed. The strength values of these concrete specimens were compared and the results were discussed. As a result; it has been determined that the concrete strengths obtained by considering the relevant standards are compatible with the literature. Thus, in this study, it has been determined that aggregates tested for use in concrete have positive effects on concrete strength.

The synergetic interaction of chemical admixtures on the properties of eco-friendly lightweight concrete from industrial technogenic waste

It is important to know how different superplasticisers (SP) types affect the rheological properties of foamed cement pastes and influence the physical and mechanical properties of eco-friendly porous lightweight aggregate concretes based on industrial technogenic waste. Three tested superplasticisers—lignosulfonates SP(S), polycarboxylates SP(C), polyacrylates SP(A), air-entraining admixture (AEA) and their combinations—differently prolong the setting time of Portland cement (OPC) pastes. The results show that SP(A) retards the setting time of OPC paste to the minimum extent both in individual use or in combination with AEA. The dynamic viscosity of OPC pastes depends on the metakaolin additive (MA) to OPC ratio and AEA. In pastes with the highest MA to OPC ratio, the dynamic viscosity is 2.46 times higher than in a paste without MA. The effect of AEA in the pastes expresses itself in increased dynamic viscosity, up to 50.8% compared to the same samples without AEA. Increasing the MA to OPC ratio in pastes with AEA and SP(A) allows entraining a higher volume of air, which results in uniform pore distribution and increasing apparent porosity by 2.2 times. Increasing the MA to OPC ratio in a eco-friendly lightweight aggregate concrete (LAC) sample creates a highly porous macrostructure, resulting in decreased density, up to 40.1%, and thermal conductivity coefficient, up to 2.1 times (from 0.152 to 0.073 W/(m·K) and increased water absorption, up to 44.8% (from 5.73% to 8.3%). With an increased MA to OPC ratio in a LAC sample series, the compressive strength decreased up to 14 times after 7 days of hardening, however, after 56 days of hardening, the tendency of increase for compressive strength is observed.

Structural performance of fiber reinforced lightweight self-compacting concrete beams subjected to accelerated corrosion

Lightweight self-compacting concrete (LWSCC) is gaining popularity since it inherits the best properties of both the lightweight concrete (LWC) and SCC. Addition of fibers to LWSCC can further enhance its performance by improving ductility, crack bridging and energy absorption capacity. However, fiber reinforced LWSCC (FRLWSCC) could have durability issues due to its relative high permeability resulting from porous lightweight aggregates (LWA). Hence, proper investigation on durability performance of FRLWSCC is essential for its long term sustainable application. Despite such importance, no significant research findings are available in literature on durability of FRLWSCC. In this study, the durability of FRLWSCC beams were investigated through accelerated corrosion testing. Both corrosion resistance and structural performance of FRLWSCC beams were evaluated. The structural response of un-corroded beams was also assessed and compared with their corroded counterparts. The FRLWSCC was prepared using three types of fibers; i.e., Polyvinyl Alcohol (PVA), Crumb Rubber (CR) and High Density Poly Ethylene (HDPE) fibers. The LWSCC-HDPE beam exhibited superior corrosion resistance as compared to LWSCC-PVA and LWSCC-CR beams. The LWSCC-HDPE beam experienced a lesser amount of mass loss of reinforcement, fewer cracks and less spalling. Moreover, it sustained the maximum residual peak load and showed higher post-cracking shear resistance.

Research on Improving Concrete Durability by Biomineralization Technology

The interfacial transition zone (ITZ) around aggregates in concrete is a weak area with higher porosity than the matrix; it breaks easily under stress and is not conducive to the durability of concrete. However, the ITZ in concrete is full of calcium hydroxide crystals, which can provide the calcium source required for biomineralization. In view of this, this study aims to use the biological activity (i.e., biomineralization technology) existing in nature to enhance the ITZ in concrete and repair concrete cracks to improve the strength and durability of concrete. In this study, the bacterial strain Sporosarcina pasteurii, which is environmentally friendly, was selected. In addition, lightweight aggregate was used as a bacterial carrier. The bacteria were first sporulated. To protect the strains, the biological species were fixed in porous lightweight aggregates. These lightweight aggregates were then used as concrete aggregates. The planned tests included concrete engineering properties (i.e., compressive strength, chloride ion penetration, and water permeability tests) and residual strength after crack repair. The test results show that the use of lightweight aggregate as a carrier and the implantation of Sporosarcina pasteurii can induce biomineralization, strengthen the ITZ, and repair small internal cracks in concrete, thereby improving the strength and durability of the concrete.

The impact of expanded polystyrene waste of different fineness on the properties of lightweight composite

Expanded polystyrene (EP) is widely used as a packaging material for many types of goods. However, once the material is used, it is disposed of in landfills, where it can remain intact for the lifetime of several generations. Recycling of disposed EP packaging is of high relevance worldwide. The main objective of this study is to make a more detailed research into the effect of EP aggregate waste of different fineness and shape on physical and mechanical properties of porous lightweight aggregates concrete (PLWAC) with EP waste aggregates. Tests were done with Portland cement, EP waste of different fractions, resulted from crushing (EPR) and cutting (EPU), metakaolin, superplasticizer and air entraining admixture. Six batches of PLWAC specimens were formed with different EPR/EPU ratios, ranging from 0.5 to 3.The change in EPR/EPU ratio in PLWAC leads to structural changes and density reduction from 550 to 410 kg/m3 after drying. When EPR/EPU ratio in the PLWAC is increased to 2, the compressive strength of the specimens drops from 2.3 to 1.75 MPa and down to 0.55 MPa, when EPR/EPU ratio is increased to 3.

Prevention of Autogenous Shrinkage in High-Strength Mortars with Saturated Tea Waste Particles.

The purpose of this study was to prevent early age autogenous shrinkage in high-strength mortars with saturated tea waste particles. In general, high strength and high performance concretes are made with low water/binder ratios; hence, they are susceptible to shrink at early ages. This shrinkage occurs due to self-desiccation that leads to autogenous shrinkage. To overcome self-desiccation problems in high-strength cement composites, it is necessary to keep the composites moist for a long time. Pre-saturated porous lightweight aggregates and super absorbent polymers are the most commonly used materials in high-strength cement composites to keep them moist for a long time; however, in this study, porous tea waste particles were used to keep the cement mortars moist. Pre-saturated tea waste particles were used in two different size proportions, making up as much as 3% of the volume of the binder. Moreover, commonly used lightweight aggregate (perlite) was also used to compare the outcomes of specimens made with tea waste particles. Different parameters were observed, such as, flow of fresh mortars, autogenous shrinkage, mechanical strengths and microstructure of specimens. The addition of tea waste and perlite particles in mortars made with Ordinary Portland cement (OPC) as the only binder, showed a reduction in flow, autogenous shrinkage and mechanical strengths, as compared to mixes made with partial addition of silica fume. Although, the use of silica fume improved the mechanical strength of specimens. Moreover, the use of saturated tea waste and perlite particles also improved the microstructure of specimens at an age of 28 days. The results revealed that the saturated tea waste particles have the ability to prevent autogenous shrinkage but they reduce strength of high-strength mortars at early ages.