Search

This paper examined how the amount (5% or 20%) and type (CaSO4 or Na2SO4) of sulphate salt affect the hydration of calcium sulphoaluminate clinker (KCSA). The mechanical behavior of the pastes was determined at 1, 3, 28, and 90 days, the heat flow and total heat were measured with isothermal conduction calorimetry, and the reaction products were characterized using X-ray diffraction (XRD), differential thermal analysis/thermogravimetry (DTA/TG) and scanning electron microscopy (SEM). The results obtained indicated that both the amount of sulphate salt (5% or 20%) and its type (CaSO4 or Na2SO4) affect the hydration kinetics, type of reaction products formed, and development of mechanical strength. The incorporation of CaSO4 has a positive effect on the development of the mechanical strength of KCSA. However, Na2SO4 can also produce adverse side effects at older ages. The presence of Na2SO4 increases pH values, which partly destabilizes the ettringite formed, thereby favoring carbonation and thenardite precipitation, which can cause the specimens to crack and break.

The primary object of the present research was to investigate the porous low calcium alkali activated material (AAM). Traditionally Na+ ions for alkali activation solution ensure highly alkaline media which enhances the dissolution of amorphous phase in the raw materials forming solid cementitious material with sodium aluminosilicate hydrate (N-A-S-H) structure afterwards. Almost all alkali ions are partially hydrated filling the pores in the gel structure (N-A-S-H gel, type zeolite precursor) and neutralizing the charge on Al(OH)-4 groups. These alkali ions are available for leaching in water environment. Due to this property the application of porous AAM in this research is related to the water treatment systems similar to those of natural zeolites which are considered as effective sorbent because of their porous structure, high specific surface and ion exchange. Porous AAM was obtained from metakaolin, sodium silicate glass, modified sodium silicate solution with Ms = 1.68 and diethylene glycol (DEG) aluminium paste as pore forming agent. The density of AAM was 1150 ± 12 kg/m3 and compressive strength fc > 12 MPa. The effect of heat treatment to microstructure and structural properties of AAM was investigated. Heat treatment is an effective method for changing the alkali leaching kinetic form AAM structure.DOI: http://dx.doi.org/10.5755/j01.ms.23.3.16280

This paper is wholly committed to resource efficiency through the valorization of waste from other industries, and more specifically fly ash as a raw material to produce concrete-like geopolymers. In particular, this study aimed to determine the effect of the physical and chemical characteristics of recycled coal fly ash used to manufacture alkaline cement on reaction kinetics and product microstructure and performance. The ash was mixed with 8 M NaOH and cured for 20 h at 85°C and RH > 90% to form a compact paste, after which mechanical strength was determined and the reaction rate was calculated using isothermal conduction calorimetry. The findings showed that vitreous content (SiO2/Al2O3), reactive and (especially) fineness play a very important role in both the development of cement mechanical strength and the composition and structure of the reaction products formed.

This work analyzes the effect of the presence of 5 wt.% of solid sodium salts (Na2SO4, Na2CO3, and Na2SiO3) on calcium sulfoaluminate cement (CSA) hydration, addresses hydration kinetics; 2-, 28-, and 90-d mechanical strength, and reaction product microstructure (with X-ray diffraction (XRD), and Fourier transform infrared spectroscopy, (FTIR). The findings show that the anions affect primarily the reactions involved. Ettringite and AH3, are the majority hydration products, while monosulfates are absent in all of the samples. All three salts hasten CSA hydration and raise the amount of ettringite formed. Na2SO4 induces cracking in the ≥28-d pastes due to post-hardening gypsum and ettringite formation from the excess SO42– present. Anhydrite dissolves more rapidly in the presence of Na2CO3, prompting carbonation. Na2SiO3 raises compressive strength and exhibits strätlingite as one of its reaction products.

The present study explores the effect of activating solution concentration (4, 6 and 8 M NaOH) on mechanically and thermally pre-treated carbonate-high illite clay (LCR). Pastes were prepared with an alkaline solution/clay (S/B) ratio of 0.55, which were cured at room temperature and relative humidity > 90% in a climatic chamber. At two and 28 days, compressive mechanical strength was determined, and the reaction products were characterised by X-ray Powder Diffraction analysis (XRPD), Fourier-transform infrared spectroscopy (FTIR) and Scanning Electron Microscopy - Energy Dispersive X-ray spectroscopy (SEM/EDX). Results obtained showed that the presence of reactive calcium in the starting clay induces co-precipitation of a mix of gels: An aluminium-enriched C-S-H gel (C-A-S-H) and a N-A-S-H gel, in which sodium is partially replaced by calcium (N,C)-A-S-H. Pastes prepared with higher (6 or 8 M) activator concentrations exhibit a more compact matrix than the ones prepared with 4 M NaOH. The findings show that the use of a 6 M NaOH solution yields a binder with two days compressive strength >20 MPa and 28 days strength of over 30 MPa.

Mine tailings (MT) could represent a step forward in terms of the quality of the aggregates usually used in civil engineering applications, mostly due to its high density. The Portuguese Neves Corvo copper mine, owned by the Lundin Mining Corporation, produces approximately 3 million tonnes per year. Nevertheless, it cannot be used in its original state, due to its high levels of sulphur and other metals (As, Cr, Cu, Pb, Zn). This paper focuses on the stabilisation/solidification of high-sulphur MT, without any previous thermal treatment, using alkali-activated fly ash (FA). The variables considered were the MT/FA ratio and the activator type and concentration. A fine aggregate was then added to the pastes to assess the quality of the resulting mortar. Maximum compressive strengths of 14 MPa and 24 MPa were obtained for the pastes and mortars, respectively, after curing for 24 h at 85 °C. Thermogravimetric analysis, scanning electron microscopy, X-ray energy dispersive spectroscopy, X-ray diffraction, and infrared spectroscopy were used to characterize the reaction products, and two types of leaching tests were performed to assess the environmental performance. The results showed that the strength increase is related with the formation of a N-A-S-H gel, although sodium sulphate carbonate was also developed, suggesting that the total sodium intake could be optimized without strength loss. The solubility of the analysed metals in the paste with 78% MT and 22% FA was below the threshold for non-hazardous waste.

Advanced-stage primary cutaneous T-cell lymphoma has an unfavorable prognosis and low survival rates. Aggressive treatment with chemotherapy is not curative and causes considerable side effects. The combination of bexarotene and denileukin diftitox is associated with an acceptable safety profile and a likely synergistic effect because bexarotene is capable of modulating expression of IL-2 receptor and enhance the susceptibility of T-cell leukemia cells to denileukin diftitox. In the case reported here, the response to this combined treatment was satisfactory and well tolerated. The patient showed a complete regression of pruritus, restlessness, and insomnia. Skin lesions improved partially, and lymphadenopathy was reduced and finally disappeared completely.

En este trabajo se presentan algunas de las propiedades tecnológicas de los materiales cementantes elaborados por activación alcalina de aluminosilicatos. Más específicamente sobre las propiedades de morteros y hormigones elaborados con cenizas volantes activadas alcalinamente (sin cemento Portland). Así en función del tipo de activador alcalino empleado y tras un curado térmico previo, el material resultante presentará una interesante lista de propiedades y características que incluyen: elevadas resistencias mecánicas iniciales (a flexión y a compresión), baja retracción al secado, y una muy buena adherencia matriz-acero, así como una excelente resistencia al ataque ácido y un excelente comportamiento frente al fuego. Es por ello que estos nuevos cementos debido a sus magnificas características tecnológicas y durables, así como a la facilidad de adecuarlos a las instalaciones existentes en la industria de los prefabricados, pueden ser fácilmente utilizados en diversas aplicaciones como por ejemplo: elaboración de durmientes para el ferrocarril, bloques para edificación o pavimentación, etc.In this paper are presented some of the technologic properties of cementitious material elaborated by alkali activation of aluminosilicates are presented. More specifically it is about the properties of alkali activated fly ash concrete and mortar (without Portland cement). So depending on the type of alkali activator that is used and after a previous thermal curing, the resulting material will show an interesting list of properties and features that includes: high initial mechanical strengths (under flexure and compression), low drying shrinkage, and a very good matrix-steel bonding, as well as an excellent strength to acid attack and an excellent behaviour when is exposed to fire. That is the reason why these new cements, due to their magnificent and durable technologic features as well as its easy adaptability to the existing installations in the precast industry, can be used in a variety of applications, for example: elaboration of railroad cross ties, blocks for building or paving, and so others.

Nowadays, the tracks that comprise the world railway network are estimated to contain nearly three billion sleepers, over 400 million of which are made of concrete. At the same time, over 50% of the world demand for sleepers (around 20 million units per year) was for the concrete version; and between 2% and 5% of the concrete ties that are laid on tracks every year are to replace or renew worn elements. Concrete durability, however, depends on many factors. And in this context it should be noted that the characteristics of the in-plant industrial process involved in manufacturing precast concrete units differs in a number of ways from in situ construction, vesting these units with properties that distinguish them, in terms of durability, from in situ concrete under the conditions generally prevailing on construction sites. Generally speaking, it is widely admitted that the activation process of fly ashes allows obtaining a material with similar cementing features to those characterising Ordinary Portland Cement. Actually, the alkali activation of fly ashes is a singular procedure by which the powder originated in the power plants is mixed with certain alkaline dissolution and cured under a certain temperature to make solid materials. Contrary to conventional concrete, however, this new type of concrete can attain high strength over a very short time (1 day) and do develop excellent durability propertiesActualmente se estima que las vías de ferrocarril a nivel mundial contienen aproximadamente tres billones de durmientes, de los cuales 400 millones son de hormigón. Conjuntamente, sobre el 50% de la demanda mundial por durmientes (estimada en 20 millones anualmente) fue por durmientes de hormigón; además, entre el 2% y 5% de los durmientes de hormigón son utilizados en reemplazar elementos dañados. La durabilidad del hormigón, sin embargo, depende de muchos factores. En este contexto se debe hacer notar que el proceso de prefabricación de elementos de hormigón industrial en planta difiere de la fabricación in-situ, lo que les da a los primeros características que los hacen destacar en términos de durabilidad. En general, se sabe que el proceso de activación de cenizas volantes permite obtener un material con características cementantes similares a aquellas del cemento Portland. En realidad, las cenizas volantes activadas con álcalis es un procedimiento singular en el cual el residuo resultante de la combustión de carbón en plantas termoeléctricas es mezclado con disoluciones alcalinas que curadas bajo ciertas temperaturas generan materiales resistentes. A diferencia del hormigón tradicional, este nuevo tipo de hormigón puede alcanzar altas resistencias en un periodo muy corto de tiempo (1 día) además de desarrollar una durabilidad excelente

This paper presents the study of the nature and conservation state of different stuccos and Roman concretes from the Roman city of Baelo Claudia (Cádiz). The chemical, mineralogical and microstructural compositions of the said materials have been established. Different causes of their decay have been found, among which we should emphasize the loss of the binding material (lime), basically due to the processes of partial solubilization; the lack of bond between the stuccos and the support stone, due to the different characteristics and properties of these two materials; and finally, the biological-type attack with the proliferation and colonization of different organisms in the said materials.

This paper constitutes a compilation as well as an interpretation of the present state of knowledge about the different microstructures developed in the interface areas of concrete, that is, the cement paste-aggregates, the cement paste-reinforcement, the cement paste-fiber, etc. The Chemical reactions taking place in interface areas, the development and morphology of such areas and their strength ^since interfaces are taken as the weakest points of concrete) are the aspects dealt with in some detail in this work.

The effect of a small quantity of CaF2 on the capacity of reaction of raw mixes has been studied in this paper; and for this purpose the thermal behaviours of a commercial raw mix without the addition of CaF2 were compared at different ages of clinkerization. The times required to complete the reactions at different temperatures are estimated. The mineralizer effect of fluorspar has a maximun at temperatures of clinkerization of about 1.200ºC and ages of cinkerization of about 10 minutes.

Five different compositions belonging to the equilibrium system CaO-Al2O3-Fe2O3 were dopep with a fixed quantity of MgO (6,5% wt). The compositions, which lie in different primary fields of crystallization and in different triangles of compatibility, were submitted to several thermal treatments. Each composition, which had previously been melted, originates in its solidification the aluminates and ferrites which are usual in the interstitial phase of clinker Portland, although they are in different microstructural arrangements. The effect of MgO on the generated microstructures has been shown. Also, the solubility of MgO on the aluminic and ferritic phases has been measured.

In this research the process of formation of a low energy clinker is studied, when fly-ashes (rich in sulphates and lime) and fluorspar are used as raw materials (fly-ashes replaces to the tradicional raw mix partially). The availability of those fly-ashes is shown since clinker at 1.340 °C is obtained. The mineralogical composition, mineralizer capacity and temperature of formation of the new liquid phase is studied.

A preheater with fluidized bed is planned on a pilot scale, capable of being fitted to a rotatory furnace, also of a pilot nature, for the manufacture of Portland clinker. With this it is intended to design a system of dynamic simulation of clinkerization, to obtain clinker of similar characteristics to those which are obtained industrially.