Cement Type CEM Research Articles

Thermo-mechanical performance of concrete with alternative binder material

Purpose – The purpose of this paper is to investigate the effect of changes to fundamental components of concrete; cement type, water/cementitious (w/c) ratio, aggregate size and age, on thermo-mechanical properties. Understanding the heat transfer properties of construction materials will enable a reduction in energy expenditure and associated CO2 emissions, contributing to a more sustainable built environment. Design/methodology/approach – Concrete specimens were subject to steady-state heat transfer test methods to determine thermal conductivity and specific heat values. Pore volume of specimens was determined using water displacement method. Findings – Cement type CEM I produced the lowest thermal conductivity values by a maximum of 30 per cent, cement type group CEM I corresponded to higher pore volumes and lower densities than cement type group CEM II. Specific heat was higher in specimens containing CEM II compared to CEM I, with cement type being the dominant factor that determines the specific heat capacity. The w/c ratio 0.55 provided lowest thermal conductivity values of the w/c ratio specimens, however, w/c ratio had no impact on the specific heat of concrete. Cement type was the most dominant component of concrete of the properties tested. Originality/value – The paper presents knowledge of the thermal performance of concrete with easily achieved changes to concrete mix design, which can be used alone or combined for maximum effect. Steady-state heat transfer techniques in a low moisture environment combined with pore volume testing, provides originality to the study of the behaviour of cement replacements as previous research has mainly been based on transient techniques. The use of steady-state heat transfer experimentation allows important thermal properties, thermal conductivity and specific heat to be calculated.

Use of calorimetry and other methods in the studies of water reducers and set retarders interaction with hydrating cement paste

The calorimetric method was used as a main tool in the studies of the effect of superplasticizing and set retarding admixtures on cement hydration. The experiments were carried out using two types of cements (neat Portland cement CEM I 42.5R and blended Portland cement type CEM II/B-M (S-V) 42.5N), at varying w/c ratio 0.5 and 0.3 respectively. The hampering of cement hydration process at early age in the presence of these admixtures was generally observed. This is in practice equivalent to the set retardation. The dissolution, as well as the precipitation of hydration products were retarded too, as it has been proved by the DTA/TG, conductometric measurements and the evaluation of so-called chemical shrinkage. However in case of superplasticizers, after a prolonged “dormant” period the process is continued; the reactions occur at fairly good rate giving substantial heat effects – it can be concluded from the total heat evolved values after standard 41h. At longer time a significant amounts of products are formed as well, but it seems that the crystallization of calcium oxide is disturbed; simultaneously the amount and composition of calcium silicate hydrates alters towards the “more amorphous” product. This could be observed under SEM. The set retarders give strong delaying effect, particularly at low amount of water and in the pastes produced from Portland cement. This can be due to the formation of insoluble layer of calcium and sugar or calcium and phosphorus containing compounds surrounding the hydrating grains; the formation of this “barrier” can be distinguished as a small peak on the calorimetric curve and it is poorly removable on further hydration. The shrinkage and conductivity measurements seem to prove not only the change of kinetics of heat evolution/hydration but also the modification of the process and resulting products.

Coal–biomass fly ashes for cement production of CEM II/A-V 42.5R

This paper presents possibilities of use of fly ashes from co-burning bituminous coal and biomass in cement production of CEM II/A-V 42.5R. Fly ashes from the 2nd and the 3rd section in electrostatic precipitator system were analysed. The following properties of fly ashes were tested: physical properties, chemical composition and pozzolanic activity. Heat of hydration and compressive strength of fly ash cements were examined. Results showed that fly ashes from the 2nd and the 3rd section can be used to obtain cement type CEM II/A-V 42.5.

Evaluación de la reactividad árido-álcali en diversos áridos silicatados. Alternativas para minimizar esta reacción

Siliceous aggregates are characterized for presenting certain chemical reactivity opposite to the calcium hydroxide liberated in the hydration of the Portland cement. The consequence of this reaction between the aggregate and the components of the intermediate concrete phase is the formation of gels very eager for water that can generate important disruptive pressures in the deeper structure of concrete. We have assessed the potential reactivity of several siliceous aggregates (granites, gneiss, hornfels, granites, quartzite and serpentine) by means of the accelerated method in concrete bars (normalized method) and the superficial reactivity method, observing by scanning electron microscopy (SEM) the formation of silica calcium alkaline gels. On the other hand, we explore the way of minimizing this disruptive reaction employing ground clay bricks and cement type CEM IV UNE-EN 197-1.

Copper Slag Mortar Properties

Copper slag is a copper industry waste that is essentially used as an abrasive for metals to remove coatings or paintings, due to its hardness, sieve distribution and rough surface, mainly in the naval industry. After the wearing process, copper slag retains most of its original properties, and remaining an environmental problem. Chemical composition of copper slag presents a high Fe, Si and Al oxide content what makes it a pozzolanic material. Thus, it is possible to use it as a partial replacement for sand and after triturating it into very small particles as a replacement for cement. After a chemical, physical, mineralogical, and environmental characterization of copper slag, its use as a partial replacement of sand on mortars was investigated. The experimental program was developed to evaluate the effect of several percentages of sand substitution in mortars. For mortars 25, 50 and 75 % of sand replacement by volume was studied. A standard 1/3 cement/sand ratio, by weight, with cement type CEM 42.5 I, was used. The type of sand and the effect of washing the slag were also investigated. Strength was measured at 7, 28, 60 and 90 days. Results obtained until now indicate that a reduction of strength occurs when the slag content increases. Additionally, it was observed a delay of the hardening process by the addition of the copper slag. As a conclusion, the use of copper slag as a sand replacement seemed to be a practical option.

Soil permeability tester

Carbonation processes cannot be ignored as regards durability and service-life of new concrete structures, and their correct understanding and quantification are essential for maintenance and repair works on existing structures. This paper initially presents a new meta-model developed to calculate carbonation front depth based on the analytic solution of Fick’s first law. The only input data required by this non numerical model are: (i) material variables (concrete mix design, maximum nominal aggregate size, cement type, and chemical composition of cement type CEM I and cement density); (ii) technological parameters (initial curing period (tc)); (iii) environmental parameters (ambient temperature (T), relative external humidity (RH) and CO2 concentration in the air ([CO2]ext)). Consequently, this model is fully suitable for the prediction of carbonation depth in the case of new reinforced concrete structures, for which these required parameters are well-known. The meta-model is validated using data from the literature on short and long-term natural carbonation exposure conditions. Most of the experimental data concern CEM I, CEM II, CEM III cement types, and CEM I additives (fly ash (FA)) with various water to cement (W/C) ratios and tc. The meta-model is also compared with two already available models: Papadakis’ model and Yang’s model. The three model predictions are compared with the corresponding values found in the literature. The results confirm that the prediction of the new meta-model proposed here for estimation of carbonation depth is the most accurate in every case.