Evaluation of Different Shrinkage Control Methods on High-Performance Concrete

Synergetic effect of superabsorbent polymer and shrinkage reducing admixture on the properties of alkali-activated slag binders

Effect of internal curing with super absorbent polymers on the relative humidity of early-age concrete

The effect of a shrinkage reducing admixture (SRA) on the mechanical properties and drying shrinkage of a proprietary alkali activated cementitous material (AACM) was investigated. Five AACM mortar mixes were prepared. SRA replaced the liquid activator at a dosage of 0%, 1%, 2%, 4% and 7%. The liquid/binder ratio was 0.38. The samples were cured in water. The flexural and compressive strengths of all mixes were determined at 1day, 2 days, 7 days and 28 days and the drying shrinkage was determined up to 80 days. The results show that SRA reduced the shrinkage of AACM mortar by up to 69% after 80 days at 7% dosage. However, SRA also reduced the compressive and flexural strengths of AACM mortars. Increasing dosages of SRA reduced the compressive and flexural strength while recording less shrinkage. Regardless of the dosage of SRA, a unique relationship exists between flexural strength and compressive strength, which correlates with the data of previous research. The AACM mortar maintained strength of over 43MPa (greater than 75% of the control mix at 0% SRA dosage) at 7% SRA dosage, which is classified as high strength in accordance with British Standard PAS 8820:2016.

Effects of temperature rising inhibitor and shrinkage reducing admixture on pore structure of early-age cement paste

The reduction of the moisture content of concrete during the drying process reduces the concrete’s volume and causes it to shrink. In general, concrete shrinkage is a phenomenon that causes concrete volume to dwindle and can lead to durability problems. There are different types of this phenomenon, among them chemical shrinkage, autogenous shrinkage, drying shrinkage including free shrinkage and restrained shrinkage, and thermal contraction. Shrinkage-reducing admixtures are commercially available in different forms. The present study investigates the effect of liquid propylene glycol ether on mechanical properties and free shrinkage induced by drying at different water-cement (w/c) ratios. Furthermore, the effect of shrinkage-reducing admixtures on the properties of hardened concrete such as compressive and tensile strength, electrical resistivity, modulus of elasticity, free drying shrinkage, water absorption, and depth of water penetration was investigated. The results indicated that shrinkage reducing agents performed better in a low w/c ratio and resulted in up to 50% shrinkage reduction, which was due to the surface reduction of capillary pores. The prediction of free shrinkage due to drying was also performed using an artificial neural network.

Study of synergistic effect of fly ash and superabsorbent polymers on properties of cement pastes

Concrete of strengths classes ≥ C55/67 referred to as high strength or high-performance concrete (HSC/HPC) are noted to be generally of low water/binder (W/B), made from binary or ternary cements with silica fume (SF) being a necessary constituent, and often requiring internal curing. Non-availability and high cost of SF in most sub-Saharan Africa like Nigeria however makes HSC/HPC production in this region very difficult and hence the continued search for alternative supplementary cementitious materials (SCM) with good performance properties as constituents of ternary/binary cements in HPC. This study thereby examines the strength properties of metastable calcined clay (MCC) based HPC cured internally with superabsorbent polymer (SAP) 0.2–0.3% (by weight of binder (bwob)). HPC mixtures of varied MCC and Rice husk ash (RHA) contents containing two SAP grain sizes labelled (SP1 ˂ 300 µm and SP2 ˂ 600 µm) were cast in 100 mm cubes and cured for varying ages (7, 14, 28 and 56 days) before testing. The hardened specimens were subjected to compressive strength and water absorption tests at the varied curing ages for the performance assessment of the binder types and SAP grain sizes in HPC with age. This study revealed the possibility of achieving Class 1 HPC (50–75 N/mm2) utilizing industry manufactured calcined clay and locally produced RHA in Nigeria. The compressive strength of HPCs increased as the curing age increases for both SCM type, SAP contents and grain sizes. RHA based HPCs however showed better strength performance at the early ages than the MCC based. SAP addition in MCC based HPCs led to slight decrease in compressive strength as the SAP contents increased while the RHA based HPCs on the other hand, revealed slight increase in compressive strength with increase in SAP contents.

Theoretically, high-performance concrete with w/c ratio about 0.30 and w/b about 0.28 should have low porosity, low water permeability and high strength. The purpose of this study was to examine the influence of the superplasticizers( with and without air-entraining effect) and shrinkage reducing admixture based on a high molecular weight basis alcohol amount on the air-content, compressive strength, shrink and resistance to water penetration of high-performance self-compacting concrete (HPSCC). The test results have shown that despite the low water content, concrete modified with inadequately selected SP and high amount of SRA has a high porosity and low strength and water permeability. The types of superplasticizers and amount of SRA are significant due to porosity parameters, compressive strength and water-permeability of HPSCC. The water permeability and compressive strength of HPSCC depending on the effects of amount of SRA admixtures on the volume of pores in HPSCC. Moreover, shrinkage of incidental air-entrained concrete, despite its lower endurance, after 28 days of hardening it is smaller than non-aerated concrete.

Editorial

Early-stage phenomena during concrete curing greatly influence its final mechanical properties, making hydration monitoring crucial. Non-destructive techniques have, therefore, gained great attention for early-age concrete assessment. This study examines the elastic wave velocity and stiffness development of hardening concrete cubes using elastic wave tomography (EWT) at different curing stages. Simultaneously, ultrasonic pulse velocity (UPV) measurements with a pseudorandom noise (PRN) pulse are performed and compared to a standardized UPV device. Monitoring begins 7 hours after mixing and continues until 70 hours. A three-dimensional (3D) velocity map compares conventional concrete with concrete containing superabsorbent polymers (SAPs), a shrinkage-reducing admixture. SAPs reduce the compressive strength of concrete by increasing the porosity, affecting the elastic wave velocity evolution. However, internal curing by SAPs promotes hydration product formation, partially offsetting strength loss. EWT provides global insights into SAP uniformity across specimens, contrasting with traditional single-path UPV measurements. Furthermore, early-age stiffness evolution, linked to UPV, is a good indicator of final mechanical properties. Results show that SAP concrete exhibits slower 3D stiffness development than conventional concrete but supports hydration over a longer period. Continuous wavelet transform (CWT) analysis of PRN signals shows prolonged signal transmission development, indicating a more thorough hydration evolution in SAP concrete.

Liquid lipase-catalyzed esterification of fatty acids with methanol is a promising process for biodiesel production. However, water by-product from this process favors the reverse reaction, thus reducing the reaction yield. To address this, superabsorbent polymer (SAP) was used as a water-removal agent in the esterification in this study. SAP significantly enhanced the conversion yield compared with the reaction without SAP. The lipase-catalyzed esterification in the presence of SAP was then optimized by response surface methodology to maximize the reaction conversion. A maximum conversion of 96.73% was obtained at a temperature of 35.25 °C, methanol to oleic acid molar ratio of 3.44:1, SAP loading of 10.55%, and enzyme loading of 11.98%. Under these conditions, the Eversa Transform lipase could only be reused once. This study suggests that the liquid lipase-catalyzed esterification of fatty acids using SAP as a water-removal agent is an efficient process for producing biodiesel.

Due to the difficulties in maintaining failing concrete structures built with normal concrete (NC), high-performance concrete (HPC), which is extremely dense and has a low water-binder content, has been developed. However, it has been observed that inadequate internal curing in HPC can lead to autogenous shrinkage and micro-cracking. Previous research has indicated that internal curing (IC) agents, such as pre-saturated lightweight aggregate (LWA) and superabsorbent polymers (SAP), are frequently used to address this issue. It is also noteworthy that the production of HPC necessitates the use of additional supplementary cementitious materials (SCM), particularly silica fume, which is not easily accessible in Nigeria or other Sub-Saharan African countries. This article presents the report of an effort to replace silica fume in HPC with millet husk ash (MHA) as a SCM material. The HPC specimens produced was internally cured with pre-soaked pumice as LWA and SAP respectively, with the view to establish the effectiveness of MHA for production of HPC. The results of 28, 56 and 90 days for concrete specimen immersed in ordinary water and in 5% of MgSO4 for C55/67 HPC mixtures for 100 mm concrete cubes having 7.5% silica fume content is compared with MHA based HPC of varied MHA contents of 2.5%, 5%, 7.5%, 10% and 15%).The results reveal 2.5%MHA performed best when compare with the control (i.e 7.5%SF) in resisting 5% MgSO4 attack with a strength loss factor of 1.89, 1.81 and 1.31% at 28, 56 and 90 days of age and was recommended for use as SCM and IC-agent in HPC.

Influence of a combination of expansive and shrinkage-reducing admixture on autogenous deformation and self-stress of silica fume high-performance concrete

Autogenous shrinkage and hydration property of alkali activated slag pastes containing superabsorbent polymer

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.