Supersulfated Cement Research Articles

A study on super-sulfated cement using Dinh Vu phosphogypsum

Super-sulfated cement (SSC) is a newly developed unburnt cementitious material. It is a kind of environmental-friendly cementitious material due to its energy-saving, carbon emission reducing, and waste-utilization. It mainly composes of phosphogysum (PG) and ground granulated blast furnace slag (GFS), with a small amount of cement. In Vietnam, the Diammonium Phosphate DAP – Dinh Vu fertilizer plant in Dinh Vu industrial zone in the northern port city of Hai Phong – has discharged millions of tons of solid waste containing gypsum after 9 years of operation. The waste has changed the color of the water, eroded metal and destroyed fauna and floral systems in the surrounding area. Notably, according to the environmental impact assessment, the gypsum landfill area is supposed to be 13 hectares and the storage time reaches up to five years. This paper presents the experimental results on SSC using a high amount of Dinh Vu phosphogypsum and GFS in comparison with those of ordinary Portland cement (PC). The results show that the setting time of SSC is much longer than that of Portland cement but the compressive strength of SSC can be obtained 45-50 MPa at the age of 28 days, similar to that of the control sample using 100% PC40, and 69MPa at the age of 90 days. This value even exceeds the compressive strength of the PC40 cement.

Hydration Properties of Ground Granulated Blast-Furnace Slag (GGBS) Under Different Hydration Environments

The hydration properties of various cementitious materials containing Ground Granulated Blast-furnace Slag (GGBS), two alkali-activated slag cements (AAS-1 and AAS-2) in which sodium silicate and sodium hydroxide act as alkaline activators respectively, supersulfated cement (SSC) and slag Portland cement(PSC), are compared with ordinary Portland cement (OPC) to investigate the effect of activating environment on the hydration properties in this study by determining the compressive strength of the pastes, the hydration heat of binders within 96 hours, and the hydration products at age of 28 days. The results show that C-S-H gels are the main hydrated products for all cementitious systems containing GGBS. Ca(OH)2 is the hydration products of OPC and PSC paste. However, ettringite and gypsum crystals instead of Ca(OH)2 are detected in SSC paste. Additionally, tobermorite, a crystalline C-S-H, and calcite are hydrated products in AAS-1. Tobermorite, cowlesite and calcite are hydrated products of AAS-2 as well. Based on strength results, AAS-1 paste exhibits the highest compressive strength followed by POC, PSC, SSC in order at all testing ages and AAS-2 give the lowest compressive strength except for the early age at 3 days, which is higher than SSC but still lower than PSC. From hydration heat analysis, alkalinity in the reaction solution is a vital factor influencing the initial hydration rate and the initial hydration rate from higher to lower is AAS-2, AAS-1, OPC, PSC and SSC. Although AAS possesses a faster reaction rate in the initial hours, cumulative hydration heat of AAS is comparably lower than that of OPC, but higher than those of PSC and SSC in turn, which indicates that the hydration heat of clinkers is much higher than that of slag.DOI: http://dx.doi.org/10.5755/j01.ms.23.1.14934

Engineering Properties and Microstructural Performance of Low Energy Super-Sulfated Cement Using Industrial Waste Anhydrite

This study aims at proposing the mix proportions of low energy super-sulfated cement (SSC) concrete from industrial waste anhydrite from circulating fluidized bed combustion (CFBC) fly ash (CFA) as an alternative sulfate activator of ground granulated blast furnace slag (GGBFS/slag). The optimized mix proportion of the SSC was carried out by using mixture of different amounts of CFA in range of 25—45 wt.% and various quantities of ordinary Portland cement (OPC) in range of 0 — 10 wt.% to trigger the hydration of slag. Experimental results showed that with the expected slump at values of 190 — 220 mm, the 28-day compressive strengths of the concrete with low energy SSC reached 43.69 MPa which can be feasibly applied for widely advanced construction materials. The OPC in range of 3 — 5 wt.% and 25 wt.% of CFA were considered as the optimum ingredients of the activator and was suggested to be used for fabricating the low energy SSC concrete with the good performance on compressive strength, dynamic Young’s modulus, UPV measurement, and stabilized change of length. The OPC additive up to 10 wt.% was encouraged to be used for producing the SSC concrete with significant reduction on creep.

Accelerated Biodeterioration Test for the Study of Cementitious Materials in Sewer Networks: Experimental and Modeling

Important deteriorations have been observed in concrete sewers, due to hydrogen sulfide (H2S) production. Hydrogen sulfide environment involves the selection of sulfur-oxidizing bacteria (bacteria able to oxidize the reduced sulfur compounds) in contact with the cementitious materials. These biological reactions lead to a local production of sulfuric acid and, as a consequence, to the dissolution of cement matrix and its mineralogical transformations (gypsum and ettringite formation). This phenomenon disturbs the sewer system and leads to expansive works of rehabilitation. As a consequence, a project was initiated in order to propose more efficient solutions. The main objectives of this project are to set up an accelerated test and to develop an associated model. To date, experimental studies and some improvements of the model previously setting up were performed. The first study describes the impact of several parameters, including type of cementitious materials, on hydrogen sulfide adsorption. These abiotic tests involve monitoring hydrogen sulfide concentration as a function of time. This experiment was realized in a hermetic chamber with five types of mortars (cast with calcium aluminate cement (CAC), blended Portland cement (CEM III, CEM IV and CEM V) and super sulfated cement (SSC)) and under different relative humidity. The second study is deterioration state of mortars characterization, thanks to some analyses (SEM – EDX). After three months of exposition, different types of sulphur species are observed on mortar surfaces, which vary with the nature of mortar. All these experiments allow providing improvements to model previously setting up. Abiotic tests measurements are used to determine mathematical law, which modelises hydrogen sulphide adsorption on each type of cementitious material.

Contrastive Numerical Investigations on Thermo-Structural Behaviors in Mass Concrete with Various Cements.

This work is a contrastive investigation of numerical simulations to improve the comprehension of thermo-structural coupled phenomena of mass concrete structures during construction. The finite element (FE) analysis of thermo-structural behaviors is used to investigate the applicability of supersulfated cement (SSC) in mass concrete structures. A multi-scale framework based on a homogenization scheme is adopted in the parameter studies to describe the nonlinear concrete behaviors. Based on the experimental data of hydration heat evolution rate and quantity of SSC and fly ash Portland cement, the hydration properties of various cements are studied. Simulations are run on a concrete dam section with a conventional method and a chemo-thermo-mechanical coupled method. The results show that SSC is more suitable for mass concrete structures from the standpoint of temperature control and crack prevention.

The Use of Supersulfated Cement(SSC)in Mass Concrete

This paper isfocused on the use of Supersulfated Cement (SSC) in mass concrete. The physicalproperties and mechanicalproperty was tested. Contrast with the common cement, this paper studied the temperature rise of hydration and the heat of hydration to obtain the advantage of SSC, which will provide the basis for the use of SSC in mass concrete.The micro properties were tested through Scanning Electron Microscope (SEM). The test shows that the SSC shows better workingperformance than ordinary cement. The compressive strength of SSC under standard curing condition is higher than that under room curing condition. The compressive strength of SSC is increasing with time and the rate of increasing is decreasing. The temperature rise of hydration of SSC are lower than that of ordinary cement. Different with the ordinary cement, the main hydrated products of SSC areettringite and scalycalcium silicate hydrate.

Formulating for Innovative Self-Compacting Concrete with Low Energy Super-Sulfated Cement Used for Sustainability Development

This study proposed a new way to formulate a low energy super-sulfated cement (SSC) which can be used to produce self-compacting concrete (SCC) with high compressive strength and durability in terms of chloride penetration resistance. This innovative SSC, different from the traditional SSC, was purely produced with a ternary mixture of three industrial by-products of ground granulated blast furnace slag, low calcium Class F fly ash and circulating fluidized bed combustion (CFBC) fly ash and was denoted as SFC-SSC (super-sulfated cement made by mixture of slag, Class F fly ash and CFBC fly ash). Experimental results showed that the combination of a fixed amount of 15 wt.% of CFBC fly ash with various ratios of Class F fly ash to slag could be used to produce the hardened SCCs with high 28-day compressive strengths (41.8 - 65.6 MPa). Addition of Class F fly ash led to the resulting SCCs with lowered price and preferable engineering properties, and thus it was considered as state-of-the-art method to drive such type of concrete towards sustainable construction materials.

Influence of curing temperature on the process of hydration of supersulfated cements at early age

In this paper, the influence of curing temperature was studied for supersulfated cements made with two slags having different chemical compositions. Supersulfated cements (SSC) made with low-alumina slag developed lower porosity, higher compressive strength and degree of hydration at higher temperatures. SSC made with high-alumina slag resulted in higher strengths and presented a more complex mechanism of hydration that was strongly influenced by the solubility of anhydrite.

Influence of fineness on hydration kinetics of supersulfated cement

Hydration heat evolution rate and quantity of supersulfated cements (SSCs) with three different specific surface areas (335m2/kg, 445m2/kg and 518m2/kg) were measured at 25°C by isothermal calorimetry. The hydration heat evolution quantity of SSCs improves with the increase of cement fineness, but is much lower than that of ordinary Portland cement. The hydration of supersulfated cement is accelerated by the elevated fineness, and the hydration process of supersulfated cement after induction period was divided into three periods, nucleation and crystal growth (NG), phase boundary reaction (I), and diffusion (D), which are well simulated through Krstulovic–Dabic model. The connecting points of NG process and I process, I process and D process both decrease with the increase of fineness which shows that the second exothermic peak is in advance. I process also decreases with the increase of fineness, which indicates that I process is accelerated by fineness. The hydration of supersulfated cement is sensitive to fineness, especially for the specific surface area reaching up to 518m2/kg.

Hydration and mechanical properties of cement/sludge/anhydrite gypsum system

Setting and hardening of fresh blends of ordinary Portland cement (OPC), fired drinking water treatment sludge (DWTS) and calcined anhydrite gypsum were investigated. Sludge or Portland cement was substituted with 5 wt%, 10 wt% or 15 wt% of anhydrite gypsum. These systems lead to the preparation of supersulfated cement. These blends were shown to possess both the advantages of gypsum (early hardening, high early strength and enhanced workability) and Portland cement (improved durability in moist conditions). The initial and final setting time, bulk density and compressive strength of cement pastes were measured. Differential scanning calorimetry, X-ray diffraction and Fourier transform infrared spectroscopy techniques were used to investigate the hydration products. Substitution of DWTS with 15% anhydrite accelerates the final setting time and increases the bulk density as well as the compressive strength. Substitution of OPC with 5% anhydrite gives the same results but extends the final setting time. It can be concluded that supersulfated cement can be prepared from samples with 10–15 wt% anhydrite substituted DWTS or from the sample with 5 wt% anhydrite substituted OPC.

The suitability of a supersulfated cement for nuclear waste immobilisation

Composite cements based on ordinary Portland cement are used in the UK as immobilisation matrices for low and intermediate level nuclear wastes. However, the high pore solution pH causes corrosion of some metallic wastes and undesirable expansive reactions, which has led to alternative cementing systems being examined. We have investigated the physical, chemical and microstructural properties of a supersulfated cement in order to determine its applicability for use in nuclear waste encapsulation. The hardened supersulfated cement paste appeared to have properties desirable for use in producing encapsulation matrices, but the high powder specific surface resulted in a matrix with high porosity. Ettringite and calcium silicate hydrate were the main phases formed in the hardened cement paste and anhydrite was present in excess. The maximum rate of heat output during hydration of the supersulfated cement paste was slightly higher than that of a 9:1 blastfurnace slag:ordinary Portland cement paste commonly used by the UK nuclear waste processing industry, although the total heat output of the supersulfated cement paste was lower. The pH was also significantly lower in the supersulfated cement paste. Aluminium hydroxide was formed on the surface of aluminium metal encapsulated in the cement paste and ettringite was detected between the aluminium hydroxide and the hardened cement paste.

Mechanical Performances of Super Sulfated Cements

Tested super sulfated cements (SSC) are composed with various amounts of ground granulated blast furnace slag, gypsum or activated gypsum and Portland cement. Our initial results on the optimization of the composition and of the curing conditions of such cements are presented herein. Tests are conducted on the basis of standard mortar with two different gauging ratios according to old and new standards for SSC. Four types of curing are used. Mechanical performances are assessed at 2, 7, 28, 60 and 90 days on standard mortar samples (binder/sand mass ratio = 1/3). This study shows that, thanks to an optimization of the Portland cement content, it is completely possible to obtain super sulfated cement with a strength class 32.5N, and always in conformity with the new European standard. For a given SSC formulation, it is clearly demonstrated that the origin of the calcium sulfate addition that affects the development of sulfo-aluminous compounds in these mixtures constitutes a key point in the phenomena of setting and hardening. The use of heat-activated gypsum as a sulfate activator appears preferable.

Mineral Foams Obtained with Super Sulfated Cement

The purpose of this study is to evaluate the performances of Super Sulfated Cement (SSC) foams, focusing on structural, thermal and mechanical characteristics. The studied set of SSC foam samples is obtained with the same slurry. The chosen foaming method allows an interesting density variation: from 489 kg/m3to 1793 kg/m3. Thanks to a CCD camera, the visual study of foam pore structure reveals two kinds of bubbles distribution and associated connectivity. This may partially explain the obtained thermal and mechanical behavior. Results show that SSC foams with low density (< 550 kg/m3) are usable as thermal insulator for non-loadbearing walls. Mean density SSC foams (550 kg/m3< - < 640 kg/m3) can be used as slight-loadbearing and thermal insulating products in housing and SSC foams with high density (640 kg/m3< - < 1200 kg/m3) as loadbearing products staying within lightweight class.

Quantification of hydration phases in supersulfated cements: review and new approaches

Quantification of the progress of hydration of supersulfated cements (SSC) may be approached in two ways: (a) from recording the increasing dissolution of the slag particles directly, and (b) indirectly from quantifying the formation of the hydration phases. Image analysis based on backscattered electron imaging in a scanning electron microscope (SEM), the dissolution of hydrates (EDTA), differential thermal analysis (DTA) and sulfide concentration (SP) were used to quantify the dissolution of the slag particles; selective extraction of hydrates by sodium carbonate (SE), X-ray diffraction (XRD) with Rietveld analysis and thermogravimetric (TGA) refinement methods were used to quantify the amount of hydration products formed. SEM-based image analysis was found to be a direct and promising way for the quantification of slag particles. With the help of selective extraction by sodium carbonate (SE), it was possible to quantify the amorphous C–S–H phase in SSC. Mass balance calculations constrained by thermodynamic stability were used to calculate the amount of reacted slag in the system. XRD Rietveld and TGA methods were used to assess the amounts of specific hydration products formed in SSC but did not allow an absolute quantification of the amount of slag reacted. Other methods such as the dissolution of the hydrates by EDTA and DTA were not found to be reliable due to intrinsic problems.