Ordinary Portland Cement Paste Research Articles

Properties and environmental assessment of eco-friendly brick powder geopolymer binders with varied alkali dosage

This paper presents the effect of alkali dosage on the mechanical properties and water resistance of alkali-activated brick powder geopolymers (BPG) by measurements of compressive and flexural strengths, bulk density, water absorption and softening coefficient. To reveal the micro-mechanism of BPG under varied alkali dosage, the mineralogical phases, reaction degree, micromorphology, and pore structure of BPG are analyzed by techniques of XRD, TGA, SEM and MIP, respectively. Furthermore, the environmental impacts of BPG are evaluated by considering CO2-e emission and energy consumption. Results show that the BPG prepared with low alkali dosage (2% or 4% Na2O) exhibits the loose microstructure with few amorphous gels and relatively high porosity (including high proportion of capillary pores) resulting in the relatively poor mechanical properties and water resistance. However, a higher alkali dosage (6% or 8% Na2O) promotes the geopolymerization reaction resulting in the denser microstructure with more amorphous gels and relatively lower porosity, thereby greatly enhancing the mechanical properties and water resistance with maximal flexural strength, compressive strength and softening coefficient of 2.2 MPa, 31.1 MPa and 0.77 respectively. Water immersion may cause Na+ and OH− to dissolve from BPG matrix resulting in a charge imbalance of three-dimensional network structures, which will further lead to strength degradation. In comparison to ordinary Portland cement paste, BPG can reduce CO2-e emission by about 40%–70% and energy consumption by about 20%–50%. The optimal mixing parameters have an alkali dosage of 6%, a silicate modulus of 1.6 and a water-to-binder of 0.3 by considering the compressive strength and environmental impacts.

Thermo-mechanical stability of supplementary cementitious materials in cement paste to be incorporated in concrete as thermal energy storage material at high temperatures

The incorporation of recycled materials in concrete as a partial replacement of cement is becoming an alternative strategy for decreasing energy-intensive and CO2 emissions imputable to the cement manufacture, while investigating new potential uses of such multifunctional materials for environmental sustainability opportunities. Therefore, low-cost and worldwide availability of by-products materials is being assessed for sensible heat thermal energy storage applications based on cementitious materials. A greater concern is especially required focusing on the thermal stability of cement paste under high temperature cycled conditions. Moreover, compatibility between cement type and supplementary cementitious materials is determinant for the proper performance reliability. In this study, benchmark cement types were selected, i.e., ordinary Portland and calcium aluminate. Six supplementary cementitious materials were added to both types of cement in a content of 10 % and 25 %. Thermo-mechanical properties were studied before and after 10 thermal cycles from 290 to 650 °C. Results after thermal cycling showed that calcium aluminate cement paste mixtures maintained their integrity. However, most ordinary Portland cement paste mixtures were deteriorated: only mixtures with 25 % cement replacement with chamotte, flay ash, and ground granulated blast furnace slag remained without cracks. Calcium aluminate cement paste mixtures obtained the highest compressive strength, for partial replacement of cement with 10 % of chamotte, ground granulated blast furnace slag, and iron silicate. The incorporation of supplementary cementitious materials did not increase the thermal conductivity.

Synergistic Effects between Carbonation and Cracks in the Hardened Cement Paste

This paper investigates the synergistic interaction between carbonation and microcracks in hardened cement pastes. Ordinary Portland cement pastes with three different water/cement ratios of 0.4, 0.5 and 0.6, hydrated for 28 days with crack apertures ranging from 10 to 150 μm were subjected to accelerated carbonation in a climate chamber that controls the targeted relative humidity (65 and 75%), CO2 concentration (0.3 vol.% and 1 vol.%) and temperature (20 °C). Mercury intrusion porosimetry, N2-adsorption and thermogravimetry analysis were used to quantify the carbonation-induced changes in pore size distribution, porosity and phase assemblages. Additionally, the changes in crack apertures were followed during carbonation. The results indicated that cracks within the investigated range facilitate the carbonation along the crack surface due to a faster gas diffusion process. The cracks with apertures below 50 μm increase the carbonation depth at least by a factor of two for all studied w/c and environmental conditions. We observed a constant increase in crack openings during carbonation and its linear relationship with the amount of precipitated calcium carbonate. Due to depletion of CH and decalcification of C-S-H close to the sample surface, the crack aperture increase becomes limited. Therefore, the crack apertures do not increase further after the material around the crack is carbonated. It was also found that the densification of the carbonated cement matrix coexists with large capillary pores (>50 nm) or cracks, especially for the low w/c samples. The shift in pore size distribution from about 100 nm towards smaller pores (4.5–50 nm) and a decrease in gel pore fractions after 28 days of carbonation also indicate a simultaneous calcium carbonate precipitation in meso/capillary pores and decalcification of C-S-H at the nanoscale.

Recycling of calcined carbonated cement pastes as cementitious materials: Proposed CCUS technology for calcium looping

In this study, calcined carbonated hydrated cement pastes (HCPs) were used to partially replace ordinary Portland cement (OPC) as a cementitious material. Calcined carbonated HCP can be derived from carbonated HCP after the release of CO2 for the carbon capture, utilization, and storage (CCUS). Calcined carbonated HCP was produced by calcining carbonated HCP at 1000 °C, also used in calcium looping. The crystal phase compositions of the HCP, carbonated HCP, and calcined carbonated HCP were identified. Various hardening and microstructural tests on the composite cement paste mixtures blended with calcined carbonated HCP were performed. The initial results showed that the HCP could sequester CO2, forming various calcium carbonates. After carbonated HCP calcination, the main nanocrystalline phases of calcium silicate hydrate (C-S-H) and calcium carbonate decomposed, forming lime and wollastonite. The 28-day compressive strength of the calcined carbonated HCP–OPC mixtures increased with the replacement ratio up to 20%, owing to the filler effect of wollastonite. The microstructural analysis revealed that the portlandite, C-S-H, and monocarboaluminate phases were formed after hydration. Finally, by recycling demolition waste, this study proposed a technology roadmap for CCUS to achieve this goal, and a life cycle assessment was conducted to evaluate and compare the environmental impacts of producing 1 t of calcined carbonated HCP–OPC mixtures and plain OPC paste.

Impact of accelerating admixtures on the electrical properties of ordinary portland cement pastes

Electrical resistivity is a reliable concrete testing tool that agencies, researchers, and contractors have adopted to quickly assess the transport properties of cementitious systems. Like other electrically-based tests, resistivity measurements can be influenced, among other factors, by the ions dissolved in the pore solution of cementitious systems. To isolate the pore solution component, some researchers have suggested the implementation of the formation factor, which accounts for the system's pore solution. Among the mixture constituents potentially affecting the pore solution, accelerating admixtures are thought to have significant effects. Due to the lack of pore solution data, the community has come to mistrust any electrically-based test performed on concrete mixtures that include this kind of admixture. This study aims to improve the understanding of the effect that four different types of accelerating admixtures have on the electrical properties of an ordinary portland cement paste system. The data show that the influence of accelerating admixtures on the pore solution lessens over time. Moreover, development rates in the degree of hydration and the porosity of the system are found to be significantly affected by the chemistry of the admixture. Both electrical resistivity and formation factor are found to have high correlation with the total porosity of systems with and without accelerating admixtures.

Cement-Biofouling and Sulfate Resistivity of Hardened Blended Cement Pastes in Marin Environment: A Case Study

In the present study, field examinations are explored on diversed blended cement mixes. The hardened blended pastes are prepared using ordinary Portland cement (OPC), fine metakaolin (MK) and brine chlorine sludge(CLS). Cement fouling features and the attack by SO4-2 ions are studied on the blended samples that are immersed in the sea water for 9 months. The performance of the cured specimens was explored via studying the compressive strength, the percent of mass change and the volume expansion at various curing durations. Besides, the total chlorophyll colonized on the surface of the cured specimens was determined by using spectrophotometeric technique. XRD and SEM techniques are specifed for studying the phase compositions and the morphology of the formed cement hydrates. The results illustrate that the blended mixes show an antifouling behavior higher than the neat OPC. This is related to acquiring a more compact structure of reduced porosities upon OPC blending. Additionally, OPC-MK specimens showed higher SO-42 ions resistance than OPC-CLS or OPC pastes. This is related to the high pozzolanic properties of MK in contrary to brine sludge.

Effects of polyurethane–silica nanohybrids as additives on the mechanical performance enhancement of ordinary Portland cement paste

Using organic–inorganic nanocomposites to control cement hydration products is a promising method to improve the mechanical properties of cement-based materials. In this work, novel silica nanohybrids with flexible polyurethane (PU) were synthesized and used as highly efficient mechanical-performance enhancement agents for cement paste. Compared to pure cement pastes, the flexural strength and compressive strength of cement pastes with PU-silica nanohybrids obviously increased at a dosage of 1.0‰. XRD, SEM, and cement-hydration tests were also conducted to explore the mechanism of PU-silica nanohybrids on cement paste. The addition of PU-silica nanohybrids led more C-S-H appeared in the cement hydration products, which was also conducive to increasing the mechanical performance of the cement paste.

Shrinkage characteristics of calcium sulphoaluminate cement concrete

Shrinkage is an important scientific and engineering issue in the study of cement concrete, involving the risk of cracking, safety and durability of the structure. For Ordinary Portland cement (OPC) concrete, capillary tension, represented by internal relative humidity, is normally considered as the main driving force of shrinkage. However, for calcium sulphoaluminate cement (CSA) concrete, it may be completely different. In the present paper, shrinkage performance of normal and high strength CSA concrete is experimentally investigated. Characteristics of shrinkage of CSA concrete comparing to OPC concrete are analyzed and the possible mechanisms are explored. The results show that development of shrinkage of CSA concrete since set obeys two-stage mode, fast growth stage before 2 h and a slowly developing stage after 2 h. In the initial 2 h after set of concrete, more than 85% of the total shrinkage at 28 days is finished. Development of internal relative humidity of CSA concrete also undergoes a moisture saturated stage and a decline stage since casting. In humidity decline stage, less than 15% of the shrinkage of 28 days is developed in the later age although the internal relative humidity is obviously decreased as well in this period. Water content and chemical shrinkage test further confirm that faster water consumption and larger chemical shrinkage are expected for CSA paste and also for CSA concrete, comparing to that of OPC paste or concrete. Hydration particle size test results reveal that the deformability of hydration products of CSA under drying is less than that of hydration products of OPC. This may partially explain why low drying shrinkage of CSA concrete is observed.

In situ pH monitoring in accelerated cement pastes

The fast pH changes in ordinary Portland cement pastes (with and without C3A), caused by the addition of an Al2(SO4)3 based setting accelerator were in situ monitored by optical pH sensors. The results obtained clearly demonstrated the ability of this novel method to determine the pH with a high temporal resolution. Additionally, the distribution of the accelerator within the cement paste was assessed by fluorescence imaging with the use of a fluorescein tracer. Instantly after the addition of the accelerator and the subsequent formation of ettringite, the pH dropped from ~13 to ~10. The pH drop and recovery rate was controlled by the accelerator dosage and availability of Ca2+ and OH−. The methods presented would help to predict and assess the effects caused by chemical admixtures (e.g. setting accelerators) on the cement hydration progress.

Enhanced carbonation curing of cement pastes with dolomite additive

AbstractCarbonation curing of cement‐based materials has recently received increasing attention as a CO2 utilization technology. This study aimed at investigating the effects of carbonation curing on the performance of ordinary Portland cement (OPC) pastes with dolomite additive (DPC). The CO2 uptake capacity, after being normalized to carbonation active components, significantly increased with larger dolomite mixing ratios. For DPC‐25% samples under 2.5 MPa curing pressure, the maximum CO2 uptake capacity reached 23.6 wt%, which was 23% higher than that of pure OPC samples under the same condition. Effects of water to solids (w/s) ratio and temperature on carbonation are two‐sided. The optimum w/s ratio for CO2 uptake capacity of DPC‐15% samples was approximately 0.20, while the optimum temperature was equal to 60℃ or higher than 60℃. The CO2 uptake capacity increased with finer particle size and higher CO2 curing pressures. Compared to large particles, smaller particles are more likely to have a better dilution effect, providing more contact surface for carbonated precipitation. From the pore structure changes perspective, carbonation products filled the interface between the dolomite and amorphous particles. DPC‐25% samples with higher dolomite mixing ratios provided more pores and pathways for gas diffusion, and exhibited a more uniform structure, thereby contributing to the highest compressive strength values of DPC‐25% samples (63.8 MPa) among all the DPC samples. These findings imply the possible feasibility of dolomite as an additive in carbonation cured building materials. © 2022 Society of Chemical Industry and John Wiley & Sons, Ltd.

Influences of CO2‐cured cement powders on hydration of cement paste

AbstractCarbonated cement pastes (CCP) can be used as stable carbon storage. In this work, CCP were systematically investigated as supplementary cementitious materials (SCMs)‐like components used in ordinary Portland cement (OPC) paste. The fully hydrated cement pastes were pulverized into powders and then exposed to different CO2 pressure conditions (i.e., 1.0, 2.0 and 2.5 MPa) for 24 h. These CCP powders were then mixed with OPC to form a new binder. Various fresh, hardened and microstructural properties of CCP powders and the mixtures were investigated. Initial results show that the CO2 sequestration level of CCP increased with the growth of CO2 pressure, and albeit a pozzolanic reaction occurred inside the mixture, the relatively higher water demand due to the use of 30% replacement of CCP led to the inferior workability and compressive strength than the control group. Finally, a conceptual model relating to the CCP‐OPC paste was proposed, facilitating the comprehension of the hydration behaviours of CCP‐OPC paste. © 2022 Society of Chemical Industry and John Wiley & Sons, Ltd.

Experimental and numerical investigation of drying rate impact on moisture loss, exchange coefficient and drying shrinkage of cement paste

Assessment of moisture content evolution and drying shrinkage is important for the long-term operation of large concrete structures. This paper evaluates the impact of size and boundary conditions in predicting mass loss and drying shrinkage of cement-based materials at ambient temperature. The authors conducted the study on ordinary portland cement paste. The size of specimens spanned from 1 mm to 36 mm. The experiments were performed in environmental scanning electron microscope (ESEM), Dynamic Vapor Sorption (DVS), climatic chamber (CC) and saturated salt solutions chambers. The mass loss, as well as drying shrinkage, have been recorded and simulated. The numerical simulations of experimental results show the drying and shrinkage models’ ability to consider size effects, which is essential when such models are validated on a thin specimen at a laboratory scale for prediction at the structural scale. The drying model is used to discuss the convection exchange coefficient between the material and the environment.For the surface exchange coefficient, both an analytical derivation and a numerical sensitivity study, especially regarding the size effect, are carried out. Then, the Biot-type dimensionless number called Surface Bulk Constant (SBC) is proposed to provide an improved understanding of the type of boundary conditions for moisture transport.

Influence of waste glass powder as a supplementary cementitious material (SCM) on physical and mechanical properties of cement paste under high temperatures

Supplementary cementitious materials (SCMs) have attracted increasing research interests due to the energy-intensive process and high greenhouse gases emissions of conventional cement. Meanwhile, large amounts of domestic wastes such as waste glass are causing serious environmental issues due to their nonbiodegradable characteristic. Thus, recycling waste glass is a sustainable way to mitigate the environmental problem, conserve natural materials, minimize landfill spaces, and save energy during the recycling production process. This paper experimentally studied the effect of using waste glass powder (WGP) as an ordinary Portland cement (OPC) supplementary material on the paste specimens at ambient temperature and after exposure to high temperatures (800 °C, 1000 °C, and 1200 °C). The physical-mechanical properties such as workability, setting time, compressive strength, and bonding strength of the OPC paste samples containing different mass contents of WGP (0%, 10%, 20%, and 30%) were investigated and discussed. The potential alkaline aggregate reaction (ASR) effect of WGP on OPC was investigated by the accelerated mortar-bar method. The results show that the addition of WGP contributed to the workability but led to prolonged setting time of the OPC paste. On the other hand, the introduction of WGP in OPC mitigated the degradation of the OPC matrix under high temperatures and could reduce the ASR effect. Therefore, the WGP could be regarded as a feasible SCM to OPC to improve the safety of OPC-based structures both at ambient and under high temperatures.

Utilizing alkali-activated materials as ordinary Portland cement replacement to study the bond performance of fiber-reinforced polymer bars in seawater sea-sand concrete

Alkali-activated materials (AAMs) are considered an eco-friendly alternative to ordinary Portland cement (OPC) for mitigating greenhouse-gas emissions and enabling efficient waste recycling. In this paper, an innovative seawater sea-sand concrete (SWSSC), that is, seawater sea-sand alkali-activated concrete (SWSSAAC), was developed using AAMs instead of OPC to explore the application of marine resources and to improve the durability of conventional SWSSC structures. Then, three types of fiber-reinforced polymer (FRP) bars, that is, basalt-FRP, glass-FRP, and carbon-FRP bars, were selected to investigate their bond behavior with SWSSAAC at different alkaline dosages (3%, 4%, and 6% Na2O contents). The experimental results manifested that the utilization of the alkali-activated binders can increase the splitting tensile strength ( ft) of the concrete due to the denser microstructures of AAMs than OPC pastes. This improved characteristic was helpful in enhancing the bond performance of FRP bars, especially the slope of bond-slip curves in the ascending section (i.e., bond stiffness). Approximately three times enhancement in terms of the initial bond rigidity was achieved with SWSSAAC compared to SWSSC at the same concrete strength. Furthermore, compared with the BFRP and GFRP bars, the specimens reinforced with the CFRP bars experienced higher bond strength and bond rigidity due to their relatively high tensile strength and elastic modulus. Additionally, significant improvements in initial bond stiffness and bond strength were also observed as the alkaline contents (i.e., concrete strength) of the SWSSAAC were aggrandized, demonstrating the integration of the FRP bars and SWSSAAC is achievable, which contributes to an innovative channel for the development of SWSSC pavements or structures.

Comparing carbide sludge-ground granulated blastfurnace slag and ordinary Portland cement: Different findings from binder paste and stabilized clay slurry

This experimental study investigated the use of combined industry by-products, carbide sludge (CS) and ground granulated blast-furnace slag (GGBS), to replace ordinary Portland cement (OPC) for the stabilization of clay slurry, aiming to increase the stabilization efficacy, reduce the cost, and mitigate the environmental impacts associated with OPC production and disposal of industrial by-products. To better understand the stabilization mechanisms, properties of CS-GGBS and OPC stabilized clay slurry are systematically evaluated and compared. Test results indicate that the unconfined compressive strength (UCS) of the optimum CS-GGBS-stabilized clay slurry is 2–4 times that of the corresponding OPC-stabilized clay slurry. However, the strength of OPC paste is 1.3–1.4 times that of the optimum CS-GGBS paste. Due to the ultra-high water content and the active clay minerals, larger amounts of Ca(OH)2 are required to reach the same pH of pore water in stabilized clay slurry specimens than in the paste. This is responsible for the greater optimum CS/(CS + GGBS) ratio in the stabilized clay slurry than in the paste. OPC hydrates much faster and consumes more water than CS-GGBS during specimen preparation, resulting in a much lower void ratio and higher strength of OPC paste. For the stabilized clay slurry, the binder contents are very low and the water-to-binder ratio is hence very high, and thus the effect of binder hydration rate on the void ratio is insignificant. The remarkably different strength discrepancy between both types of stabilized clay slurry is not attributed to the slightly different void ratio, but due to the significantly different microstructures formed in the stabilized materials. The findings in this study contribute to a deep insight into the strength development of stabilized clay-slurry type dredged material.

Effect of natural carbonation on chloride binding behaviours in OPC paste investigated by a thermodynamic model

The combined effects of carbonation and chloride attack can accelerate the degradation of reinforced concrete (RC) structures. In this study, the effect of natural carbonation on the chloride binding behaviours in Ordinary Portland cement (OPC) paste was investigated. The phase-equilibrium model for the dissolution/precipitation reactions and the surface complexation model for the ionic adsorption of C–S–H were adopted. An experiment from the literature was used as the benchmark. The results indicate that Kuzel's salt is produced when OPC paste is exposed to a mild chloride attack. During the natural carbonation process, Kuzel's salt is converted into Friedel's salt. As the carbonation continues, the Friedel's salt disappears. Complete natural carbonation results in a total loss of chemical binding capacity, and only a partial loss of the physical binding capacity in cement-based materials. This completely differs from the accelerated carbonation commonly used in the laboratory, which can cause complete loss of both chemical and physical binding capacity. Therefore, the durability design of RC structures vulnerable to the combined attack of chloride and carbonation based on the results of the accelerated carbonation is conservative.

Effect of Ornamental Stone Waste Incorporation on the Rheology, Hydration, Microstructure, and CO2 Emissions of Ordinary Portland Cement.

The ornamental stone industry generates large amounts of waste thus creating environmental and human health hazards. Thus, pastes with 0–30 wt.% ornamental stone waste (OSW) incorporated into ordinary Portland cement (OPC) were produced and their rheological properties, hydration kinetics, and mechanical properties were evaluated. The CO2 equivalent emissions related to the pastes production were estimated for each composition. The results showed that the paste with 10 wt.% of OSW exhibited similar yield stress compared to the plain OPC paste, while pastes with 20 and 30 wt.% displayed reduced yield stresses up to 15%. OSW slightly enhanced the hydration kinetics compared to plain OPC, increasing the main heat flow peak and 90-h cumulative heat values. The incorporation of OSW reduced the 1-, 3-, and 28-days compressive strength of the pastes. Water absorption results agreed with the 28 days compressive strength results, indicating that OSW increased the volume of permeable voids. Finally, OSW incorporation progressively reduced the CO2 emission per m3 of OPC paste, reaching a 31% reduction for the highest 30 wt.% OSW content. Overall, incorporating up to 10 wt.% with OSW led to pastes with comparable fresh and hardened properties as comported to plain OPC paste.

Characteristics of Ordinary Portland Cement Paste Containing Rice Husk Ash and Conplast

An experimental investigation on rice husk ash (RHA) and Conplast SP 430 (CP-admixture) was carried out to evaluate their effects on the paste characteristics (soundness, consistency, initial and final setting times). The cement content used was 300g and the brand was ‘Ashaka’ Portland cement conforming to BS EN 12 1973. Various combinations of the mixtures OPC-RHA-CP-admixture were used to establish performance characteristics of the pastes. Statistical characteristics, and linear regression models (no-transformation, λ = 0.5, and Box-Cox transformation) were developed on the experimental data for decisions on their performances.

Optimization of Printing Parameters for Printing of Ordinary Portland Cement using a Custom-made 3D Printer

3D printing techniques have recently received a lot of attention as a new technique for forming construction materials, due to benefits over the traditional cast. In this research, ordinary Portland cement (OPC) paste was formed using a 3D extruder. Optimized mixture and printing parameters were determined. Compressive strengths of the printed and the traditionally casted OPC paste were measured after the specimens were cured in saturated limewater for 7, 14 and 28 days, respectively. The result led to the conclusion that the most suitable mixture for printing was achieved at the water to cement ratio of 0.35 with water reducing and retarding admixture added. The optimum printing parameters were the printing speed of 60 mm/min and the feed rate of 120 ml/s. Compressive strength of the 5 x 5 x 5 cm3 hollowed and filled cubic printed specimens, were compared with casted cement paste. The strengths of both the printed and the casted specimens were higher with longer curing durations. The highest levels of strength were achieved at 12.36 MPa on the printed specimens and 80.88 MPa when testing the casted samples.

Effect of silica fume on cement rheology properties in presence of superplasticisers

The effect of silica fume (SF) at different mass concentrations (0, 2, 4, 6, 8 and 10%) on the ordinary Portland cement (C) paste rheology, in the presence of superplasticisers, has been studied. The shear stress versus shear rate was obtained by using the rheometer AR 2000. Two types of superplasticisers (PCEs) have been conducted which are acrylic copolymer (PA) and modified polycarboxylate (PC), and the saturation point of each one was 2% on the amount of cement. The water-cement ratio is equal to 0.35 (W/C = 0.35). The rheological properties of which have been defined applying a rotational viscometer with co-axial cylinders were yield stress, consistence, behavior index and thixotropy. The thixotropy was evaluated by hysteresis loop test which was performed on paste specimen with 6% of SF at 10, 40 and 70 min. The rheological behavior of cement and C-SF solutions was shear-thinning with yield stress. The flow curves were modelled by Hurshel-Bulkly (H-B) law (R2 > 0.99). Hence, it has been noted that the fluidizing effect of the organic additives on cement pastes is conditioned by the presence of silica fume addition. The yield stress and apparent viscosity of the mixtures were increased significantly by raising SF amount. In fact, the yield stress and consistency values were higher for samples added to with SF than for samples without SF. In addition, the results indicated that the PC-admixture effect on the C-SF paste fluidity is more than the PA-admixture one. In other hand, the C-6% SF mixture presented a slight thixotropy value in presence of PC-admixture in comparison with PA-admixture thixotropy especially at 70 min.