Juan Lizarazo-Marriaga

Effect of Steel Slag and Portland Cement in the Rate of Hydration and Strength of Blast Furnace Slag Pastes

This paper presents an experimental study of the influence of steel basic oxygen slag (BOS) and ordinary portland cement (OPC) on the compressive strength and the hydration mechanisms of blended grounded granulated blast furnace slag (GGBS) pastes. The compressive strength, the mineralogical changes due to hydration, the setting times, the alkalinity of the raw materials, and the pore solution, and the volume stability were measured on binary and ternary mixes. It is concluded that the steel slag can be used as an activator of GGBS and the optimum composition of those materials was determined with a proposed parameter called “slag index.” The properties measured in blended OPC-GGBS-BOS mixes showed encouraging results to be used industrially. The mechanisms of hydration of the blended slag mixes are discussed and a hydration model of the blended system GGBS-BOS is proposed.

Acid Corrosion of Plain and Reinforced Concrete Sewage Systems

The infrastructure of concrete sewage systems is affected notably by biogenic sulfuric acid attack, which causes rapid deterioration of each of its components. To provide a better understanding of this mechanism of damage, this paper reports on research carried out to study the response of the cementitious concrete matrix and the reinforcement steel under the attack of sulfuric acid. Concrete industrial pipes were cast using ordinary portland cement and pulverized fly ash, and specimens obtained from the mixes were left for several cycles in a solution of sulfuric acid at different pH. Experiments were carried out to assess the loss of weight and the electrical corrosion potential. Results showed that sulfuric acid attack can be considered a surface phenomenon, in which the acid attack destroys the cover of concrete before it reaches the reinforcement.

Steel corrosion assessment by electrochemical impedance on metakaolin blended mortars

Since Corrosion of reinforcing steel in concrete is the cause of major economic losses, Portland cement has been traditionally replaced by cements blended with pozzalanic materials, most of which have been found to reduce the corrosion of steel. This paper shows the results of an experimental research aimed to investigate the corrosion of reinforcement in mortar using electrochemical impedance spectroscopy (EIS). For this, concrete laboratory samples containing a 0.0055 m steel bar and prepared with just ordinary Portland cement (OPC) and metakaolin at a replacement level of 20% were analyzed. In order to accelerate the steel corrosion process, all the samples were kept in a 3% NaCl solution and a constant anodic electrical potential was applied. Variations in the water to cementitious material ratio (0.5 and 0.6) and metakaolin proportion were analyzed, while the cementitious material to sand ratio was kept constant at 1:2.25 in all of the specimens. The results showed a reduction in corrosion rates when metakaolin was used as a blending admixture, especially at water to cementitious material ratio of 0.5.

Isolation and Potential Biocementation of Calcite Precipitation Inducing Bacteria from Colombian Buildings

Microbiological induced calcium carbonate or calcite precipitation (MICP) has become a highly researched issue due to its multiple applications in the construction industry, being a promising alternative with a great biotechnological importance. In this work, potential calcite precipitation inducing bacteria were isolated from mortar and concrete samples of different buildings at the National University of Colombia. Eighteen crystal-precipitating strains were recovered in Urea-CaCl2 solid medium. The 16S rRNA gene sequencing identified isolates as Arthrobacter, Psychrobacillus and Rhodococcus genera. It is reported, for the first time, the calcite precipitation by P. psycrodurans and R. qingshengii. Optical microscopy and Scanning Electron Microscopy showed crystals with irregular and spherical shapes, and beige and white colours. Furthermore, crystals formation appeared to be strain-specific. X-Ray diffraction analysis confirmed crystals composition as CaCO3. Biocementation tests showed that MICP treatments of mortar cubes using P. psycrodurans caused an increase in their compressive strength compared to control samples. The positive action of a native MICP strain in mortar blocks biomineralization is shown, which is of great interest and potential for the construction industry.

Modelling chloride penetration in concrete using electrical voltage and current approaches

This paper reports a research programme aimed at giving a better understanding of the phenomena involved in the chloride penetration in cement-based materials. The general approach used was to solve the Nernst-Planck equation numerically for two physical ideal states that define the possible conditions under which chlorides will move through concrete. These conditions are named in this paper as voltage control and current control. For each condition, experiments and simulations were carried out in order to establish the importance of electrical variables such as voltage and current in modelling chloride transport in concrete. The results of experiments and simulations showed that if those electrical variables are included as key parameters in the modelling of chloride penetration through concrete, a better understanding of this complex phenomenon can be obtained.

Application of nanosilica particles under limited dispersal conditions in cement-based paste and mortar mixtures

Abstract This paper assesses the influence of nanosilica particles (in low dosages) under limited dispersal conditions on some properties of pastes and mortars made out of conventional cement (without the use of plasticizers). For this, characterisation of mixtures in fresh and hardened states were carried out through setting times, fluidity, early compressive strength and scanning electron microscopy tests. As results, flowability of the analysed mortars was higher when the silica nanoparticles were larger in size, and consequently lower flowability values were obtained for the smaller nanoparticles. It was not possible to determine an optimum content of nanoparticles since no significant increases in the early compressive strength of mortars were achieved. The obtained results in this research show that for mortars with water/cement ratio of .55 a minimum nanosize and a high amorphous content of silica particles are not sufficient to enhance mechanical strengths, but mainly a better dispersion in the cementitious matrices should be guaranteed using plasticizing admixtures in order to optimise workability and mechanical performance.

Respuesta a pulsos galvanostáticos del acero embebido en concretos de escoria activada alcalinamente

In this paper is presented the application of the galvanostatic pulse measurement which occurs in the activated slag concrete, submitted to accelerated carbonation processes. As reference material, we used ordinary Portland cement. Using the galvanostatic pulse technique enabled us the resistances values calculation which were involved separately in the carbonation process, allowing to find the corrosion rate by the Stern and Geary equation. The corrosion products were determined by the technique of Mossbauer Spectroscopy, corresponding to magnetite, goethite and wuestite.