GCP Applied Technologies (United States)

Cross-linked polymers with covalent adaptable networks (CANs) can be reprocessed under external stimuli owing to the exchangeability of dynamic covalent bonds. Optimization of reprocessing conditions is critical since increasing the reprocessing temperature costs more energy and even deteriorates the materials, while reducing the reprocessing temperature via molecular design usually narrows the service temperature range. Exploiting CO2 gas as an external trigger for lowering the reprocessing barrier shows great promise in low sample contamination and environmental friendliness. Herein, we develop a type of CANs incorporated with ionic clusters that achieve CO2-facilitated recyclability without sacrificing performance. The presence of CO2 can facilitate the rearrangement of ionic clusters, thus promoting the exchange of dynamic bonds. The effective stress relaxation and network rearrangement enable the system with rapid recycling under CO2 while retaining excellent mechanical performance in working conditions. This work opens avenues to design recyclable polymer materials with tunable dynamics and responsive recyclability. Cross-linked polymers with covalent adaptable networks are reprocessed under external stimuli at high temperatures which might deteriorate their performance. Here, the authors introduce carbon dioxide responsive ionic clusters into covalent adaptable polymer networks to facilitate the exchange of dynamic bonds providing materials with a rapid recycling and good mechanical performance.

Abstract The use of pre-hydrated cement in formulation of mortar and concrete is common because there is not always effective control on the cement production, grinding, transportation and subsequent storage. This paper presents a case study on the optimization of admixture for use with prehydrated cement by assessing changes in the rheological properties of Portland cement artificially pre-hydrated. The cement was artificially pre-hydrated by exposure to relative humidity (RHs) of 90%, in an environment of NH4Cl saturated solution. Additionally, the cement pastes were evaluated with and without superplasticizer. Stepped flow test using a parallel-plate geometry was the method choose to evaluate the rheological behavior, apparent viscosity, yield stress and hysteresis area of each paste at the early age. Oscillatory rheometry was conducted to evaluate the storage modulus (G’), comparing the consolidation with the hydration kinetics obtained by calorimetric evaluation of the same suspensions. Initial rheometer results indicate that the pre-hydrated sample presents lower level of shear stress than the reference sample, because of the higher reactivity of the non-pre-hydrated sample.

Prepared by the Post-Earthquake Fire Hazard Task Group of the Fire Protection Committee of the Structural Engineering Institute of ASCE

The relationship between the water to cement (w/cm) ratio of a cement-based matrix and its capillary porosity is well documented. It is also well documented that this relationship extends to light intensity of the cement paste matrix using the fluorescence technique. It is also well reported that for 28-day-old portland cement–only (PC-only) concrete mixes hydrated under normal conditions, this relationship is reliable for w/cm ratio assessments between 0.35 and 0.70. This study confirmed that a similar linear relationship exists with concrete mixes containing various supplementary cementitious materials (SCMs) with differing w/cm ratios. It also showed, however, a consistently higher fluorescence developed at 28 days of age with these various SCM-containing mixes when compared with the equivalent PC-only references. The light intensity of the various SCM mixes appeared to relate more to the relative amounts of SCM material and to a lesser degree the material’s apparent translucency or coloration. Finally, this paper described the findings from a set of companion test samples produced at a greater age (18 months), which showed that the same linear relationship between w/cm ratio and fluorescent light intensity existed for all the mixes and showed that, in most cases, the differences between SCM-containing mixes and the equivalent PC-only mixes was reduced. The 18-month-old samples containing SCMs, however, still exhibited a greater fluorescent light intensity than the equivalent PC-only samples. This finding underscored the absolute requirement for appropriate reference samples when applying this technique to mixes containing SCMs.

Sand, whether natural or manufactured, shows in many instances varying degrees of high levels of clay contamination. This fact is encountered in different parts of the globe and can lead to serious problems in adjusting concrete mix proportions and requiring high water to cement ratios and/or high dosages of superplasticizers without necessarily meeting the workability requirements, even when the sand is previously washed with fresh water. In this paper, different types of sand from the Gulf Cooperation Council (GCC) region are being screened, analysed for their clay contents and consequent effects on plastic concrete quality. A technical solution is being proposed based on engineered superplasticizers. A testing protocol has been established to verify the robustness of optimized mix designs demonstrating the performance of the admixture in terms of initial and extended workability. In particular, it will be demonstrated that the customized concrete admixtures constitute by themselves a stand-alone answer to the usage of clay-contaminated sands in concrete.

A need exists in the grouting industry to define the necessary steps in successful soil stabilization by chemical grouting. Although some excellent research was done by Reuben Karol in the latter part of the 20th century, the majority of technique used today is a mixture of conjecture, rules of thumb, and misinformation. To address this need, a reproducible method for demonstrating the reaction within a sand soil matrix when injected with polyurethane grout was developed. Stabilization of sandy soils with polyurethane grout was investigated at a mock-up scale, representative of in-situ field conditions. Qualitative parameters were established for the predictability of the size and shape of the grout formations in sand based soils using various delivery techniques. Within the paper, the resulting differences in grout mass formation were examined for delivery by probe pipes, strainer pipes and tube-a-manchettes. Several methods of pumping to determine the effect of constant pressure on the resultant grout formation were explored. A protocol for presenting a mock-up scale was demonstrated. This paper is being submitted to Track B/Properties of Grouted Materials.

Abstract The phase behavior of poly(ethylene oxide) (PEO) in aqueous salt solutions has been studied many times but rarely for solution conditions relevant to the hydration process of cement, where PEO's interactions with surrounding ions modulate its application as both plasticizer and strength‐building additive. Here, the conformation, that is, coil size, of PEO was examined in aqueous solutions in the presence of sodium‐, calcium‐ and aluminum‐containing salts. Ion‐induced conformational changes for a model linear PEO were mostly unremarkable and consistent with past reports. However, trends for aluminum‐containing ions, which predominantly occur in water at neutral and basic pH as the monovalent hydroxo‐aluminate anion Al(OH) 4 − , were different: either present as the sodium or calcium salt, PEO's hydrodynamic radius determined by dynamic light scattering was approximately 30% larger than determined by intrinsic viscosity. The intrinsic viscosity was similar to that measured in the presence of simpler monovalent anions. We hypothesize that aluminum containing ions weakly couple the model polymer's hydroxyl end groups (present at just one chain end), creating polymeric aggregates sensitive to disruption by shearing. Supporting our argument, the hydrodynamic radius determined by dynamic light scattering dropped to the intrinsic viscosity value after hydroxyl groups were converted to methoxy groups.

Polyurethane and acrylate resins are routinely injected into soils to gain strength and control water flow. However, most published data regarding these materials’ performance are derived from laboratory samples created under ideal conditions. In this study, a large container was filled with a silty SAND (SM) to simulate in situ soil conditions frequently found in Vancouver, BC, and British Columbia’s Lower Mainland. The injection pressures, volumes, lift heights, and other details have been compiled to evaluate this methodology for permeation grouting. In situ and laboratory testing will be used to verify the material performance and the strength of the soil/resin composite. Dynamic cone penetrometer (DCP), Consolidated Isotropically Undrained Triaxial (CIU), Unconfined Compressive Strength (UCS), and Direct Simple Shear (DSS) testing have been performed on the polyurethane and acrylate soil composites. The soil type, compaction methods, injection methods, and testing performed have been documented and are presented in the final paper. Initial testing results indicate considerable strength gain with polyurethane treated soil versus untreated soil and the applicability of acrylate treatment in support of soil excavation projects.

Chlorinated solvents, such as tetrachloroethylene and trichloroethylene, are among the most widespread groundwater and surface-water contaminants in the United States. As the construction industry continues to build larger and deeper buildings into the water table, there is a growing probability that the pre-applied water mitigation systems used in these buildings will be exposed to contaminated groundwater and soils over the course of their service life. Understanding how different membranes and contamination exposure affect the chemical permeation rate is essential to being able to predict the waterproofing's long-term performance as a chemical barrier and ensure indoor air quality is not affected. Using existing standards as a reference, we developed a method to measure the chemical permeation rate of the below-grade waterproofing membranes at different temperature and concentration gradients. This method can accelerate the evaluation process, especially with low-permeable membranes, which typically require longer evaluation times. In addition, this method enables the analyst to build a correlation between chemical permeation rate, temperature, and time. Thus, the method presented herein provides a new way to compare the long-term performance of different membranes and can play an important role in the design of water-mitigation systems for buildings.

Polymers with dynamic bonds, often termed associating polymers, have been attracting great research interest in recent years because of their unique viscoelastic properties, self-healing ability, and recyclability. A variety of dynamic covalent and noncovalent chemistries have been explored with respect to their capabilities to form transient bonding in polymer networks. This chapter presents the recent progress achieved in studying the dynamic bonds in associating polymer networks, including fundamental understanding of the relaxation and morphology of these bonds, as well as the emerging design of dynamic polymer materials with the superior performance and energy-related applications. Models that explain the mechanisms of network rearrangement have been demonstrated for the telechelic polymer systems, along with the discussion of the effects from backbone and end-group chemistry, chain length, molecular weight, and cluster topology. This chapter will inspire readers/researchers to develop new dynamic polymer systems with advanced dynamic features.

The increasing price and diminishing reserves of natural sand and aggregates signify the urgency to develop a costeffective and eco-friendly alternative, helping the transition towards a circular economy. The ever-increasing amounts of waste glass stockpiled across Australia and worldwide (that offers nil residual value when landfilled) could offer a potential solution to this dilemma. That is, if optimally designed for reuse, waste glass utilization can promote environmental sustainability and closed-loop recycling of waste glass by decreasing the pressure on landfills, reducing the carbon footprint and conserving natural aggregates. This research aims to understand the applicability of crushed waste glass in shotcrete production. Several mix designs with up to 50% of sand replacement were prepared and tested according to standard recommendations. Mechanical strength and fracture properties of the new mix designs are compared and reported in this study against the controlled mixes at 0% waste glass inclusions.

This paper presents the results of laboratory and field experiments conducted for a major ground support operation to assess the performance of wet-mix shotcrete incorporating various chemical admixtures. The project had an alkali-silica reaction (ASR) risk due to the aggregates available in the region being reactive. Therefore, a customised mix design was prepared and specialty chemical admixtures formulated with the latest available technologies were selected to mitigate the ASR while meeting the project specifications. The performance of the proposed system, which contained 25% fly ash and 0.8% of pozzolanic-based rheology control agent, was compared with the reference mix containing 8% silica fume as well as the target performance limits of the project. Test results showed that, when compared to the reference mix, the proposed system improved the shotcrete performance by reducing the ASR potential, increasing early-age strength, enhancing sprayability by increasing the stickiness and cohesiveness, and meeting later-age strength, toughness, and durability requirements.