On the Interaction between Superabsorbent Hydrogels and Cementitious Materials

Autogenous shrinkage induced cracking is a major concern in high performance concretes (HPC), which are produced with low water to cement ratios. Internal curing to maintain high relative humidity in HPC with the use of an internal water reservoir has proven effective in mitigating autogenous shrinkage in HPC. Superabsorbent polymers (SAP) or hydrogels have received increasing attention as an internal curing agent in recent years. A key advantage of SAP is its versatility in size distribution and absorption/desorption characteristics, which allow it to be adapted to specific mix designs. Understanding the behavior of superabsorbent hydrogels in cementitious materials is critical for accurate design of internal curing. The primary goal of this study is to fundamentally understand the interaction between superabsorbent hydrogels and cementitious materials. In the first step, the effect of chemical and mechanical conditions on the absorption of hydrogels is investigated. In the second step, the desorption of hydrogels in contact with porous cementitious materials is examined to aid in understanding the mechanisms of water release from superabsorbent hydrogels (SAP) into cementitious materials. The dependence of hydrogel desorption on the microstructure of cementitious materials and relative humidity is studied. It is shown that the capillary forces developed at the interface between the hydrogel and cementitious materials increased the desorption of the hydrogels. The size of hydrogels is shown to influence desorption, beyond the known size dependence of bulk diffusion, through debonding from the cementitious matrix, thereby decreasing the effect of the Laplace pressure on desorption. In the third step, the desorption of hydrogels synthesized with varied chemical compositions in cementitious materials are investigated. The absorption, chemical structure and mechanical response of hydrogels swollen in a cement mixture are studied. The effect of the capillary forces on the desorption of hydrogels is investigated in relation to the chemical composition of the hydrogels. In the second set of experiments of this part, the behavior of the hydrogels in a hydrating cement paste is monitored by tracking the size and morphology evolution of hydrogels interacting with the cement paste matrix. It is shown that the changes on the surface characteristics of hydrogels as a result of interactions with the pore solution and cement particles can affect the desorption rate of hydrogels in contact with a porous cementitious material. Scanning electron microscopic (SEM) examination demonstrates two different desorption modes with distinct morphologies of hydrogels depending on the chemical composition of hydrogels. The effect of the interfacial bonding between the hydrogels and the cementitious matrix and its relation to the desorption is illustrated. The desorption of hydrogels with different chemical compositions in blended cement mixture containing different supplementary cementitious materials (SCMs) such as slag, fly ash, silica fume and two types of glass powders, are examined. The absorption/desorption kinetics of hydrogels in different hydrating blended cement mixtures are monitored by freeze drying the samples at different times. The surface characteristics of different hydrogels after interaction with pore solution, cement particles and SCMs particles are examined and their relation to interfacial bonding is illustrated. It is shown that different SCMs can cause distinct changes on interfacial bonding. The understanding of hydrogel behavior in cementitious materials helps with accurate mixture design for internal curing. The kinetics of desorption is crucial for the purpose of internal curing. The understanding of release mechanisms and the change in the hydrogel morphology is important for the self-healing and self-sealing applications. Two major contributions of this research are (1) to show the effect of capillary forces developed at the interface between cementitious matrix and hydrogel which can increase the rate of desorption dramatically and (2) to illustrate the chemo-physical interaction between cement pore solution and hydrating particles with hydrogels which can affect the interfacial bonding between hydrogel and cement. These two main contributions will be useful to understand the absorption and desorption behavior of hydrogel in cementitious materials. Two main strengths of experimental procedures of this research are (1) use of in-house synthesis of hydrogels that permits establishing a link between the chemical composition of hydrogels and their behavior in cementitious materials and (2) use of freeze drying for the first time to monitor the behavior of hydrogels interacting with a hydrating cementitious matrix

The usability of waste polyethylene terephthalate (PET) products obtained by polimerization in asphalt concretes

Bu çalışmada bitüm katkı maddeler ile modifiye edilerek bitüm ve bitümlü karışımların performansının iyileştirilmesi amaçlanmıştır. Bu doğrultuda pet şişeleri (polietilen tereftalat ? PET) kimyasal bir prosesten geçilerek katkı maddeleri elde edilmiştir. Katkı maddeler sıvı (ince akışkan poliol) ve katı (viskoz poliol) şeklinde olarak ve %1, %2, %3, %5, %10 oranlarında bitüme ilave edilip konvansiyonel (penetrasyon testi, yumuşama noktası testi, düktilite testi) ve superpave (dönel viskozite, dinamik kayma reometresi (DSR), çubuk eğme reometresi (BBR)) testleri ile incelenmiş, ayrıca agrega-bitüm karışımındaki etkileri Marshall stabilite testi, Nicholson soyulma testleri ile birlikte irdelenmiştir.Our purpose in this study is modifying bituminous by adding additive materials to improve the performance of bituminous and bituminous mixtures. In this regard our additive materials are acquired from pet bottles (Polyethylene terephthalate ? PET) through a chemical process. Additive materials are used in the form of fluid (tiny fluid Polyol) and solid (viscose Polyol) by %1, %2, %3, %5, %10 percentage added to bituminous and with conventional (penetration tests, softening point tests, ductility tests) and superpave examination (viscosity tests, dynamic shear rheometer (DSR) tests,bending beam rheometer (BBR) tests) also the effect of aggregate-bituminous mixture with (Marshall tests and Nicholson stripping tests) were investigated

On the Interaction between Superabsorbent Hydrogels and Blended Mixtures with Supplementary Cementitious Materials

This article studies the interactions between hydrogels with two distinct chemical compositions and hydrating blended mixtures containing supplementary cementitious materials (SCMs), including Class F fly ash, slag, and silica fume. The effect of SCMs on the absorption behavior and chemical characteristics of hydrogels was investigated. The desorption of hydrogels in hydrating blended pastes was examined at various times using scanning electron microscopy. A reduction in the absorption of hydrogels was observed in the blended slurry with fly ash compared to other slurries. Hydrogels showed faster desorption in the paste with silica fume and delayed desorption in the paste with fly ash. This was attributed to faster densification of the microstructure and development of the capillary suction in the paste with silica fume and delayed densification in the paste with fly ash at early ages

Desorption of superabsorbent hydrogels with varied chemical compositions in cementitious materials

This paper examines the desorption of hydrogels synthesized with varied chemical compositions in cementitious materials. The absorption, chemical structure and mechanical response of hydrogels swollen in a cement mixture were studied. The effect of the capillary forces on the desorption of hydrogels was investigated in relation to the chemical composition of the hydrogels. In the second set of experiments, the behavior of the hydrogels in a hydrating cement paste was monitored by tracking the size and morphology evolution of hydrogels interacting with the cement paste matrix. It was shown that the changes on the surface characteristics of hydrogels as a result of interactions with the pore solution and cement particles can affect the desorption rate of hydrogels in contact with porous cementitious materials. Scanning electron microscopic examination demonstrated two different desorption modes with distinct morphologies of hydrogels depending on the chemical composition of hydrogels. The effect of the interfacial bonding between the hydrogels and the cementitious matrix and its relation to the desorption is illustrated

On the Effect of Chemical Composition on the Desorption of Superabsorbent Hydrogels in Contact with a Porous Cementitious Material

The behavior of poly(sodium acrylate-co-acrylamide) copolymer hydrogels with varied chemical compositions in artificial pore solutions with three different pH values is examined. The absorption, chemical characteristics, mechanical stiffness, and desorption of the hydrogels in contact with a porous cementitious material were investigated. It was observed that the surface characteristics of the hydrogels play an important role in the desorption of hydrogels due to the capillary forces. It was shown that in the hydrogel systems studied here, the bonding between the hydrogels and the porous cementitious material is improved with an increase in the content of acrylamide in the hydrogels, and this results in an increased desorption rate of the hydrogels

The influence of superabsorbent polymer on the properties of alkali-activated slag pastes

•SAP showed higher absorption in extracted pore solution from AAS pastes than PC paste.•Desorption of hydrogel was delayed in AAS paste activated with Na2CO3 compared to AAS paste activated with NaOH or PC paste.•Addition of SAP was effective to reduce autogenous shrinkage in AAS pastes and PC paste. This paper discusses the interaction between superabsorbent polymer (SAP) and alkali-activated slag pastes and the influence of SAP on the properties of the pastes. SAP showed higher absorption in pore solutions extracted from alkali-activated slag pastes compared to that extracted from portland cement paste. Hydrogel desorption in alkali-activated slag matrix activated with Na2CO3 was noticeably delayed compared to alkali-activated slag matrix activated with NaOH matrix or portland cement matrix; this is attributed to a significant delay in the solid skeleton development in this matrix. Addition of SAP was shown to be effective in reducing autogenous shrinkage in alkali-activated slag pastes. A general reduction in compressive strength and electrical resistivity was observed in alkali-activated slag pastes when SAP was added; macrovoid formation and increased overall water/binder are possible reasons for this reduction, respectively

Effect of Hydrogels Containing Nanosilica on the Properties of Cement Pastes

The effect of hydrogels containing nanosilica (NSi) on the autogenous shrinkage, mechanical strength, and electrical resistivity of cement pastes was studied. The interaction between the hydrogels and the surrounding cementitious matrix was examined using thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The addition of hydrogels decreased autogenous shrinkage in the cement pastes and this reduction showed a dependence on the concentration of NSi in the hydrogels. Compressive strength and electrical resistivity were reduced in the cement pastes with hydrogels and this reduction was decreased with increased concentration of NSi in the hydrogel. A change in the phase composition of the cement paste in the region close to the hydrogel was noted, compared to the region away from the hydrogel. In a lime solution with increased pH and temperature, Ca(OH)2 and CaCO3 were found to form within the hydrogels; evidence of calcium-silicate-hydrate (C-S-H) formation in the hydrogels with NSi was obtained, indicating the possible pozzolanic potential of the hydrogels with NSi

The Behavior of Superabsorbent Polymers (SAPs) in Cement Mixtures with Glass Powders as Supplementary Cementitious Materials

The absorption and desorption of superabsorbent polymers (SAPs) in cement mixtures containing two different glass powders as supplementary cementitious materials are examined in this paper. Two SAPs with different chemical compositions were synthesized in-house and used in the experiments. SAP absorption was investigated directly through the mass change of SAPs in cement slurries, as well as indirectly using the flow test. Scanning electron microscopy was used to monitor the desorption of SAPs using samples prepared with freeze-drying. Hydration and setting time were evaluated to explain the desorption behavior of SAPs. SAP absorption generally increased in pastes with glass powders. The desorption rate of SAPs in different pastes was shown to correlate with the onset of solid skeleton development in the pastes. The addition of SAPs reduced autogenous shrinkage in neat cement paste more than in pastes with glass powders

The influence of the chemical composition of hydrogels on their behavior in cementitious materials

This study examines how the chemical composition of hydrogels influences the behavior of hydrogels in cementitious materials. A stark contrast in the behavior of some hydrogels in extracted cement pore solution, where cement particles are excluded, and in cement mixture was observed. The observed contrast was attributed to the chemical processes between the hydrogel and cement particles, which are excluded in the extracted pore solution. This finding raises concerns regarding the accuracy of hydrogel absorption measurements using only the extracted pore solution to determine the absorption of hydrogels in cement paste. The effect of hydrogels with different chemical compositions on the hydration, electrical resistivity, autogenous shrinkage, and strength of cement paste was evaluated and discussed