Hydration behaviour of sulphoaluminate belite cement in the presence op various calcium sulphates

Cement and Concrete Composites

Londoño-Zuluaga

Torre

et al. 2016

This work deals with the hydration of a calcium sulfoaluminate (CSA) eco-cement prepared with bassanite and different additives (type and content) at a fixed water/CSA ratio of 0.5. Pastes prepared with bassanite show high water demands, high viscosity values and short initial setting times which are related to the fast dissolution rate of bassanite and the subsequent precipitation of gypsum. These facts have a dramatic effect onto the mechanical strength values, and make necessary the addition of additives.Here, the addition of different amounts of specific retarders (polycarboxylate, tartaric acid and phosphonic acid) not only improved the workability of pastes and mortars, but also delayed the setting time, by modifying the dissolution rates of the phase(s), and improved mechanical strengths.Finally, mortars with high compressive strengths (46 and 84 MPa at 1 and 7 days of hydration, respectively) and, chiefly, tailored setting times with high strengths have been prepared.

Section: Introductionmentioning

confidence: 99%

“…1. The quantity of precipitated ettringite at early ages depends on the solubility of the calcium sulfate (gypsum, anhydrite or bassanite) [9,10,11,12,13]. Hence, the selection of the sulfate source (type and amount) is a key point to achieve the desired properties, mainly at early ages [9,12,13].…”

Section: Introductionmentioning

confidence: 99%

Tailored setting times with high compressive strengths in bassanite calcium sulfoaluminate eco-cements

Cement and Concrete Composites

Londoño-Zuluaga

Torre

et al. 2016

“…All these properties are related to the resulting hydration phases at the first hours of hydration. Early hydration of CSA cements [12,13] gives ettringite also named as AFt (C 6 AS 3 H 32 ), and monosulfate also known as AFm (C 4 ASH 12 ) [14], as main crystalline phases, depending mainly upon the sulfate availability. CSA binders may show variable compositions, but all of them contain ye'elimite, also called Klein's salt or tetracalcium trialuminate sulfate (C 4 A 3 S) [1,15].…”

Section: Introductionmentioning

confidence: 99%

Hydration studies of calcium sulfoaluminate cements blended with fly ash

Cement and Concrete Research

Torre

León‐Reina

et al. 2013

170

The main objective of this work is to study the hydration and properties of calcium sulfoaluminate cement pastes blended with fly ash (FA) and the corresponding mortars at different hydration ages. Laboratory X-ray powder diffraction, rheological studies, thermal analysis, porosimetry and compressive strength measurements were performed. The analysis of the diffraction data by Rietveld method allowed quantifying crystalline phases and overall amorphous contents. The studied parameters were: i) FA content, 0, 15 and 30 wt.%; and ii) water addition, water-to-CSA mass ratio (w/CSA = 0.50 and 0.65), and water-to-binder mass ratio (w/b = 0.50). Finally, compressive strengths after 6 months of 0 and 15 wt.% FA [w/CSA = 0.50] mortars were similar: 73 ± 2 and 72 ± 3 MPa, respectively. This is justified by the filler effect of the FA as no strong evidences of reactivity of FA with CSA were observed. These results support the partial substitution of CSA cements with FA with the economic and environmental benefits.

“…Hereafter cement nomenclature will be used: C = CaO, S = SiO 2 , A = Al 2 O 3 , F = Fe 2 O 3 , S = SO 3 , T = TiO 2 and H = H 2 O. BCSA cements are based on belite (C 2 S), ye'elimite (also called Klein's salt or tetracalcium trialuminate sulfate (C 4 A 3 S)) and other minor phases, such as ferrite (C 4 AF) [9][10][11][12][13] or calcium aluminates (C 12 A 7 ) [14] and calcium sulfate (CSH x ) as set retarder. The hydration of BCSA cements strongly depends on the amount and reactivity of the added calcium sulfate [15] and the presence of minor phases. Most of the hydration heat is released within the first 12-24 h of hydration [11,16,17].…”

mentioning

confidence: 99%

“…Most of the hydration heat is released within the first 12-24 h of hydration [11,16,17]. The Cement and Concrete Research 56 (2014) [12][13][14][15][16][17][18][19] water demand needed for a complete hydration process is determined by the amount of calcium sulfate and silicates. The required water/ cement ratio is slightly higher than that for OPC (for complete hydration).…”

mentioning

confidence: 99%

In-situ early-age hydration study of sulfobelite cements by synchrotron powder diffraction

Álvarez-Pinazo

Cuesta

Cement and Concrete Research

et al. 2014

Eco-friendly belite calcium sulfoaluminate (BCSA) cement hydration behavior is not yet well understood. Here, we report an in-situ synchrotron X-ray powder diffraction study for the first hours of hydration of BCSA cements. Rietveld quantitative phase analysis has been used to establish the degree of reaction (α). The hydration of a mixture of ye'elimite and gypsum revealed that ettringite formation (α~70% at 50 h) is limited by ye'elimite dissolution. Two laboratory-prepared BCSA cements were also studied: non-active-BCSA and active-BCSA cements, with β-and α′ H -belite as main phases, respectively. Ye'elimite, in the non-active-BCSA system, dissolves at higher pace (α~25% at 1 h) than in the active-BCSA one (α~10% at 1 h), with differences in the crystallization of ettringite (α~30% and α~5%, respectively). This behavior has strongly affected subsequent belite and ferrite reactivities, yielding stratlingite and other layered phases in non-active-BCSA. The dissolution and crystallization processes are reported and discussed in detail.