This study investigated the hydration characteristics and strength development of calcium sulfoaluminate-belite (CSAB) cements incorporating calcium carbonate (CC) powders with various particle size ...distributions and different gypsum amounts. In general, the CSAB hydration was accelerated by the CC powder, but the acceleration and resulting strength improvement were more effective with finer CC powder. Regardless of the fineness of the CC powder, it took part in the hydration of CSAB cement, forming hemicarboaluminate and monocarboaluminate phases. These hydration and nucleation effects compensated for the strength reduction from decreased cementing components (i.e., dilution effect) when finer CC powders were used, while they did not overcome the strength reduction when coarser CC powder was used. On the other hand, increasing the amount of gypsum for a given CC content improved the strength. The strength of CSAB cement had a clear inverse relationship with its total pore volume measured by mercury intrusion porosimetry (MIP). Thermodynamic modeling for CSAB cement hydration showed that the use of CC powder increased total volume of solid phases up to 6 wt % at a given amount of gypsum.
•Properties of CSAB cement were investigated with different water and gypsum content.•Thermodynamic modeling based on QXRD results was conducted to explore the hydration.•Increasing water promoted ...hydration, but lowered the strength development of pastes.•Gypsum played a role in controlling the hydration of ye’elmite as well as belite.•Strätlingite formation depended on a water content and a kinetic effect of hydration.
The main objective of this study was to investigate the phase and strength development of calcium sulfoaluminate-belite (CSAB) cement pastes with different amounts of gypsum and water. Thermodynamic modeling and a series of experiments including X-ray diffraction (XRD), thermogravimetric analysis, isothermal calorimetry, and compressive strength tests were performed. Decreasing the mixing water increased the strength of CSAB pastes, but decreased the degree of hydration. Interpretation of the early age XRD results and thermodynamic modeling suggested the formation of a meta-stable phase from the hydration of belite, possibly C-(A)-S-H, which transformed into strätlingite at later ages only in the samples with high water content, likely due to easier diffusion of ions at higher w/c. Furthermore, the XRD results and thermodynamic modeling confirmed that the amount of gypsum controls the hydration of ye’elimite as well as belite in the CSAB cements.
Suspensions of synthetic ye'elimite (C4A3S¯) in a saturated gypsum (CS¯H2) and calcium hydroxide (CH) solution were examined in-situ in a wet cell by soft X-ray transmission microscopy and ex-situ by ...scanning electron microscopy. The most voluminous hydration product observed was ettringite. Ettringite commonly displayed acicular, filiform, reticulated, and stellate crystal habits. Additionally, pastes with C4A3S¯, 15% CS¯H2, and varying amounts of CH were prepared and examined with X-ray diffraction (XRD) and isothermal calorimetry. The XRD experiments showed that increasing CH content caused more solid solution (SO42−/OH−) AFm phases to form at early ages (<1d) and more monosulfate to form at later ages (>1d). Calorimetry indicated that the increased production of solid solution AFm was accompanied with an increase in the initial (<30min) rate of heat evolution, and increasing CH generally reduced the time till the second maximum rate of heat evolution due to the formation of ettringite and monosulfate.
Six calcium sulfoaluminate-based cementitious systems composed of calcium sulfoaluminate, calcite, vaterite, and gypsum were cured as pastes and mortars for 1, 7, 28 and 84days. Pastes were analyzed ...with X-ray diffraction, thermogravimetric and differential thermal analyses. Mortars were tested for compressive strength, dimensional stability and setting time. Furthermore, pastes with a water/cementitious material mass ratio of 0.80 were tested for heat evolution during the first 48h by means of isothermal conduction calorimetry.
It has been found that: (1) both calcite and vaterite reacted with monosulfoaluminate to give monocarboaluminate and ettringite, with vaterite being more reactive; (2) gypsum lowered the reactivity of both carbonates; (3) expansion was reduced by calcite and vaterite, irrespective of the presence of gypsum; and (4) both carbonates increased compressive strength in the absence of gypsum and decreased compressive strength less in the presence of gypsum, with vaterite's action more effective than that of calcite.
A novel calcium carbonate cement system that mimics the naturally occurring mineralization process of carbon dioxide to biogenic or geologic calcium carbonate deposits was developed utilizing carbon ...dioxide-containing flue gas and high-calcium industrial solid waste as raw materials. The calcium carbonate cement reaction is based on the polymorphic transformation from metastable vaterite to aragonite and can achieve >40 MPa compressive strength. Due to its unique properties, the calcium carbonate cement is well suited for building materials applications with controlled factory manufacturing processes that can take advantage of its rapid curing at elevated temperatures and lower density for competitive advantages. Examples of suitable applications are lightweight fiber cement board and aerated concrete. The new cement system described is an environmentally sustainable alternative cement that can be carbon negative, meaning more carbon dioxide is captured during its manufacture than is emitted.
Calcium sulfoaluminate–belite (CSAB) cements are promoted as sustainable alternatives to portland cement because of their lower energy and CO
2 emissions during production and comparable performance. ...However, the formation of ettringite, the main hydration product in CSAB cements, can be expansive, sometimes resulting in cracking. The factors controlling expansive behavior in CSAB cements have not been completely elucidated. In this study, three CSAB cements synthesized from reagent-grade chemicals with varied phase compositions were examined for dimensional stability in water and sulfate solutions. The interdependent effects of C
4A
3Ŝ (Ye'elimite) content, calcium sulfate content, water-to-cement ratio, and particle fineness on CSAB cement expansion were evaluated. The results show that the expansive behavior can be controlled by altering chemical and physical factors in CSAB clinker, cement, and paste.
This study investigated the material properties and hydration characteristics of calcium sulfoaluminate cement (CSA) based mortars cured under 3 different initial curing temperatures. Two CSA cements ...with different M-values were selected. Obtained experimental results of mechanical properties, dimensional stability, and heat release were explained by hydration characteristics from X-ray diffraction, thermal gravimetric analysis, porosimetry, and thermodynamic modeling. Decomposition of ettringite decreased compressive strength but re-formation of ettringite after additional curing at 30 °C helped to recover the strength in CSA cement with a high amount of calcium sulfate. CSA cement with a low amount of calcium sulfate which was designed to predominantly have monosulfate as the main hydration product, showed increased 1-day strength after higher temperature curing but this occurred was at the expense of decreased 28-day strength.
Novel living shoreline methods are being developed to minimize negative environmental impact while maintaining strength and effectiveness in high-energy systems. The “Pervious Oyster Shell Habitat” ...(POSH) is a novel structure composed of oyster shells bound by a thin layer of Portland cement into the shape of a dome. The structure’s makeup greatly reduces its environmental impact while providing optimal substrate for the provision of oyster reef habitat. Previous laboratory testing has demonstrated that the structure is robust, and this follow-up study assesses the structure’s performance in the estuarine environment. Oyster and barnacle densities were compared between POSH modules and the industry standard “Oyster Ball” model Reef BallTM along two energetic shorelines in northeast Florida. Oyster densities on the POSH were high and significantly greater than on the Oyster Ball at both sites. Barnacle densities did not differ between structures and did not appear to affect oyster recruitment. The size distribution of oysters on POSH and Oyster Ball modules was measured to assess the demographics and growth of oysters over time. Overall, demographics were similar among the two structures. Differences in oyster densities and demographics were greater at our more energetic site. Results show that the POSH can be an optimal structure for early oyster recruitment and reef development in energetic systems and should be considered by restoration stakeholders.
•NP and LP increased water demand, and NP increased setting time, whereas LP did not.•NP and LP enhanced the hydration reactions in the blended cement pastes.•The pastes with LP formed hemi- and ...mono-carbonates as secondary hydration products.•NP participated in pozzolanic reactions as indicated by a reduction of CH with time.•NP and LP were found to alter the formation of ettringite and monosulfate.
The replacement of Portland cement (PC) with either supplementary cementitious material (SCM) or fillers, such as natural pozzolans (NP) or limestone powder (LP) respectively, is known to affect the chemical properties of concrete, thus influencing its fresh and hardened properties. This study investigated the effects of volcanic ash NP or LP on setting time, normal consistency, hydration, and strength properties of cement paste and mortar while following the chemical changes that were a direct result of the substitution. While both materials were found to increase water demand, NP at 30% and 50% replacement levels increased setting time while LP at 15% replacement level insignificantly influenced the property. At a proportion lower than their replacement levels, both materials reduced the ultimate compressive strength of mortar. Thermal, chemical and microstructural analyses confirmed the participatory roles of NP and LP in controlling reaction kinetics and forming new hydration products.
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