Controlling ettringite precipitation and rheological behavior in ordinary Portland cement paste by hydration control agent, temperature and mixing

Self Cite

The control of rheological properties is gaining in importance to meet the special requirements for cementitious materials in novel technologies such as 3D‐printing. A deeper understanding of the underlying mechanisms of cement hydration is necessary to customize the mix design to the specific application.The hydration of OPC is mainly characterized by the silicate and aluminate reaction. The aluminate reaction is especially relevant for the early rheological development, whereas the formation of C‐S‐H (silicate reaction) is responsible for the later hardening of the hydrating paste.A hydration control agent is used to delay the initial aluminate reaction to a defined point in time. When no additional mixing occurs during this period of rapid ettringite precipitation, the cement paste stiffens to a solid cement stone. However, when the sample is mixed during this period, the workability of the paste is retained. The rheological changes can be correlated directly to the magnitude of ettringite formation. Additionally, the compressive strength and pore size distribution of all systems (reference, HCA, HCA with additional mixing) are investigated to analyze the long‐term properties. These results predict future customized mix designs in various application fields.

Section: Correlation Between Ettringite Precipitation and Rheologymentioning

confidence: 90%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Tailored rheological development in OPC systems by controlled ettringite precipitation and its effect on compressive strength

Jakob,

Jansen,

Pott

et al. 2023

Self Cite

“…At low temperatures (i.e., 15°C), the effect of chemical admixtures decreases, which produces a dominant effect of attractive forces between cementitious particles and, therefore, higher increase of the storage modulus. In contrast, at high temperatures (i.e., 35°C) there is a higher rate of early hydration products [38], which also increases the storage modulus.…”

Section: Rheological Propertiesmentioning

confidence: 95%

Temperature dependance of 3D printed concrete produced with copper tailings

Eugenin,

Cuevas,

Navarrete

2023

Abstract3D printed concrete is being applied in an increasing amount worldwide. While in theory, there are environmental and economic benefits associated with using this technology, in practice, the amount of cement in printable concrete is much higher than in a conventional one, leading to increased environmental and economic costs. Furthermore, cement's performance relies heavily on climate variables, specifically temperature. One way to solve this issue is to include local alternative low‐CO2 materials, such as processed mine tailings, as cement replacement. This paper presents an experimental approach to assess the use of copper tailings as cement replacement in printable concrete under different ambient temperatures. Three levels of cement volume replacement have been researched. The copper tailings' rheological effect has been measured using standard printability tests and a rheometer. Four mixtures have been printed in a controlled‐climate chamber to evaluate print‐ability, buildability and extrudability. The mechanical effect has been assessed with compressive and flexural strength tests of samples collected from the printed specimens. The results show that copper tailings are a promising alternative to cement in printable concrete in countries where this by‐product is abundant.

“…Consequently, the sulfate depletion peak occurs before the silicate reaction resulting in an aluminate/silicate imbalance and a retarded silicate peak [29]. The dissolution of C3A, the dissolution of the sulfate carrier, and the rapid precipitation of ettringite [30] affect the magnitude of the initial heat flow event. Therefore, we conclude that the initial heat flow maximum is driven by the ettringite formation, i.e., more C3A and sufficient sulfate lead to more ettringite and more heat.…”

Section: Model Cement Reactivitymentioning

confidence: 99%

C₃A Variation in Synthetic Model Cements ‐ Influence on Rheology and Reactivity

Axthammer,

Ordynska,

Gädt

2023

The amount of early ettringite crystallization is known to influence the rheology of cementitious materials. It is dependent on various factors, e.g., the reaction temperature, the chemical composition of the cement and the amount of PCE. In this study, we investigate the rheology and reactivity of synthetic model cements with different contents of C3S, C3A and β‐hemihydrate (β‐HH). Their reactivity is studied using in‐situ calorimetry and their rheology is studied using a rotational rheometer. Our results demonstrate that higher C3A contents in the clinker increase the early heat release of the cements which is associated with an increased formation of ettringite. Increased C3A contents from 2.5 wt.% to 12.5 wt.% enhance the early heat by four orders of magnitude. The static yield stress of the different cement pastes was determined with an oscillation based rheometry method 17 minutes after contact with water. Interestingly, the static yield stress increases exponentially with the heat of hydration. These findings have implications for the understanding of OPC hydration, as well as for chemical optimization and the design of OPC‐based materials.