Formulation of low clinker blended cements and concrete with enhanced fresh and hardened properties

Boscaro, Federica; Palacios, Marta; Flatt, Robert J.

doi:10.1016/j.cemconres.2021.106605

Cited by 24 publications

(15 citation statements)

References 33 publications

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“…Provided the same W/C ratio is used as what is planned for the concrete, there should be a good correlation between mortars and concretes. Correlations between heat release and compressive strength as reported by [ 19 , 20 , 21 ] may be used at this stage, as these may help to adjust the water content, if needed. In addition to these tests, for the mix to be pumpable and self-compacting, a particular range of yield stress and apparent viscosity must be aimed for.…”

Section: Methodsmentioning

confidence: 99%

Additive Digital Casting: From Lab to Industry

Lloret-Fritschi

Quadranti²,

Scotto³

et al. 2022

Materials

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Concrete construction harms our environment, making it urgent to develop new methods for building with less materials. Structurally efficient shapes are, however, often expensive to produce, because they require non-standard formworks, thus, standard structures, which use more material than is often needed, remain cheaper. Digital fabrication has the potential to change this paradigm. One method is Digital Casting Systems (DCS), where the hydration of self-compacting concrete is controlled on the fly during production, shortening the required setting time and reducing hydrostatic pressure on the formwork to a minimum. This enables a productivity increase for standard concrete production. More importantly, though, it enables a rethinking of formworks, as the process requires only cheap thin formworks, thus, unlocking the possibility to produce optimised structural members with less bulk material and lower environmental cost. While DCS has already proven effective in building structural members, this process faces the challenge of moving into industry. This paper covers the next steps in doing so. First, we present the benchmark and expectations set by the industry. Second, we consider how we comply with these requirements and convert our fast-setting self-compacting mortar mix into a coarser one. Third, we present the next generation of our digital processing system, which moves closer to the industrial requirements in terms of size and the control system. Finally, two prototypes demonstrate how DSC: (a) increases standard bulk production by 50% and (b) can be cast into ultra-thin formworks. We discuss the results and the short-term industrial concerns for efficiency and robustness, which must be addressed for such a system to be fully implemented in industry.

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Section: Methodsmentioning

confidence: 99%

Additive Digital Casting: From Lab to Industry

Lloret-Fritschi

Quadranti²,

Scotto³

et al. 2022

Materials

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“…The key current disadvantage of BCs is their low hydration rate at early ages, leading to poor mechanical performances at three days of hydration or earlier. Therefore, there is a clear need to increase the reactivity of these cements, which is shared by many other low-CO 2 cements [ 5 , 6 ], such as blends of PCs with SCMs [ 2 , 3 , 7 , 8 ]. These binders usually have low mechanical strengths at early hydration ages because of the slow rate of the pozzolanic reaction(s).…”

Section: Introductionmentioning

confidence: 99%

Portland and Belite Cement Hydration Acceleration by C-S-H Seeds with Variable w/c Ratios

et al. 2022

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The acceleration of very early age cement hydration by C-S-H seeding is getting attention from scholars and field applications because the enhanced early age features do not compromise later age performances. This acceleration could be beneficial for several low-CO2 cements as a general drawback is usually the low very early age mechanical strengths. However, the mechanistic understanding of this acceleration in commercial cements is not complete. Reported here is a contribution to this understanding from the study of the effects of C-S-H gel seeding in one Portland cement and two belite cements at two widely studied water–cement ratios, 0.50 and 0.40. Two commercially available C-S-H nano-seed-based admixtures, i.e., Master X-Seed 130 and Master X-Seed STE-53, were investigated. A multi-technique approach was adopted by employing calorimetry, thermal analysis, powder diffraction (data analysed by the Rietveld method), mercury intrusion porosimetry, and mechanical strength determination. For instance, the compressive strength at 1 day for the PC (w/c = 0.50) sample increased from 15 MPa for the unseeded mortar to 24 and 22 MPs for the mortars seeded with the XS130 and STE53, respectively. The evolution of the amorphous contents was determined by adding an internal standard before recording the powder patterns. In summary, alite and belite phase hydrations, from the crystalline phase content evolutions, are not significantly accelerated by C-S-H seedings at the studied ages of 1 and 28 d for these cements. Conversely, the hydration rates of tetracalcium alumino-ferrate and tricalcium aluminate were significantly enhanced. It is noted that the degrees of reaction of C4AF for the PC paste (w/c = 0.40) were 10, 30, and 40% at 1, 7, and 28 days. After C-S-H seeding, the values increased to 20, 45, and 60%, respectively. This resulted in larger ettringite contents at very early ages but not at 28 days. At 28 days of hydration, larger amounts of carbonate-containing AFm-type phases were determined. Finally, and importantly, the admixtures yielded larger amounts of amorphous components in the pastes at later hydration ages. This is justified, in part, by the higher content of amorphous iron siliceous hydrogarnet from the enhanced C4AF reactivity.

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“…Current global levels of clinker substitution are around 30%. Chemical admixtures such as superplasticizers and accelerators have been identified to play a key role to reach higher clinker replacements while preserving the overall mechanical performance [1,2].…”

Section: Introductionmentioning

confidence: 99%

Influence of Accelerating Admixtures on the Reactivity of Synthetic Aluminosilicate Glasses

et al. 2022

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This research aims at gaining a further understanding of the impact of accelerating admixtures on the reactivity of supplementary cementitious materials (SCMs), which are widely used as a clinker replacement in blended cements. This was done on synthetic glasses with controlled composition and structure that mimic two types of real SCMs (slag and calcium-rich fly ash). The effects of DEIPA, TIPA, NaSCN and Na2S2O3 on the glass dissolution, hydration kinetics and reaction products were investigated. The obtained results concluded that the pH of the NaOH solution and the composition of the synthetic glass play a key role on the effect of the admixtures. In 0.1 M NaOH (pH = 13.0), all the studied admixtures inhibited the dissolution of slag-like glasses while they enhanced the dissolution of Ca-rich fly ash-like glasses, being Na2S2O3 the admixture that led to the highest increase of the dissolution rate of the Ca-rich fly ash-type glasses. In 1 M NaOH solutions (pH = 13.8), only the alkali admixtures (NaSCN and Na2S2O3) enhanced the degree of reaction of both glasses. In slag-type glasses pastes mixed with 1 M NaOH, the addition of 2% Na2S2O3 induced the highest increase of their reactivity as inferred by the total heat release and the amount of bound water. This is related to the formation of a high amount of S(II)-AFm, in addition to C-A-S-H, that would increase the aluminium undersaturation of the pore solution and consequently the further dissolution of the glass.

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Formulation of low clinker blended cements and concrete with enhanced fresh and hardened properties

Cited by 24 publications

References 33 publications

Additive Digital Casting: From Lab to Industry

Additive Digital Casting: From Lab to Industry

Portland and Belite Cement Hydration Acceleration by C-S-H Seeds with Variable w/c Ratios

Influence of Accelerating Admixtures on the Reactivity of Synthetic Aluminosilicate Glasses

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