José Marcos Ortega

Long-Term Behaviour of Fly Ash and Slag Cement Grouts for Micropiles Exposed to a Sulphate Aggressive Medium

Nowadays, one of the most popular ways to get a more sustainable cement industry is using additions as cement replacement. However, there are many civil engineering applications in which the use of sustainable cements is not extended yet, such as special foundations, and particularly micropiles, even though the standards do not restrict the cement type to use. These elements are frequently exposed to the sulphates present in soils. The purpose of this research is to study the effects in the very long-term (until 600 days) of sulphate attack in the microstructure of micropiles grouts, prepared with ordinary Portland cement, fly ash and slag commercial cements, continuing a previous work, in which these effects were studied in the short-term. The microstructure changes have been analysed with the non-destructive impedance spectroscopy technique, mercury intrusion porosimetry and the “Wenner” resistivity test. The mass variation and the compressive strength have also been studied. The impedance spectroscopy has been the most sensitive technique for following the sulphate attack process. Considering the results obtained, micropiles grouts with slag and fly ash, exposed to an aggressive medium with high content of sulphates, have shown good behaviour in the very long-term (600 days) compared to grouts made with OPC.

Influence of Silica Fume Addition in the Long-Term Performance of Sustainable Cement Grouts for Micropiles Exposed to a Sulphate Aggressive Medium

At present, sustainability is of major importance in the cement industry, and the use of additions such as silica fume as clinker replacement contributes towards that goal. Special foundations, and particularly micropiles, are one of the most suitable areas for the use of sustainable cements. The aim of this research is to analyse the effects in the very long-term (for 600 days) produced by sulphate attack in the microstructure of grouts for micropiles in which OPC (ordinary Portland cement) has been replaced by 5% and 10% silica fume. This line of study is building on a previous work, where these effects were studied in slag and fly ash grouts. Grouts made using a commercial sulphate-resisting Portland cement were also studied. The non-destructive impedance spectroscopy technique, mercury intrusion porosimetry, and Wenner resistivity testing were used. Mass variation and the compressive strength have also been analysed. Apparently, impedance spectroscopy is the most suitable technique for studying sulphate attack development. According to the results obtained, grouts for micropiles with a content of silica fume up to 10% and exposed to an aggressive sulphate medium, have a similar or even better behaviour in the very long-term, compared to grouts prepared using sulphate-resisting Portland cement.

Influence of curing conditions on the mechanical properties and durability of cement mortars

Real structures are hardened in conditions different from the optimum laboratory conditions, where materials are usually tested. The different temperature, and especially the different relative humidity present in the environment, may cause a different microstructure and, as a consequence, different service properties. In this work mortars made with two different cement types are tested in laboratory conditions and at a lower relative humidity. These new environmental conditions cause a slower microstructural development and different durability and mechanical properties at early hardening ages.

Performance of Sustainable Fly Ash and Slag Cement Mortars Exposed to Simulated and Real In Situ Mediterranean Conditions along 90 Warm Season Days

Nowadays, cement manufacture is one of the most polluting worldwide industrial sectors. In order to reduce its CO2 emissions, the clinker replacement by ground granulated blast–furnace slag and fly ash is becoming increasingly common. Both additions are well-studied when the hardening conditions of cementitious materials are optimum. Therefore, the main objective of this research was to study the short-term effects of exposure, to both laboratory simulated and real in situ Mediterranean climate environments, on the microstructure and durability-related properties of mortars made using commercial slag and fly ash cements, as well as ordinary Portland cement. The real in situ condition consisted of placing the samples at approximately 100 m away from the Mediterranean Sea. The microstructure was analysed using mercury intrusion porosimetry. The effective porosity, the capillary suction coefficient and the non-steady state chloride migration coefficient were also studied. In view of the results obtained, the non-optimum laboratory simulated Mediterranean environment was a good approach to the real in situ one. Finally, mortars prepared using sustainable cements with slag and fly ash exposed to both Mediterranean climate environments, showed adequate service properties in the short-term (90 days), similar to or even better than those in mortars made with ordinary Portland cement.

Short-Term Behavior of Slag Concretes Exposed to a Real In Situ Mediterranean Climate Environment

At present, one of the most suitable ways to get a more sustainable cement industry is to reduce the CO2 emissions generated during cement production. In order to reach that goal, the use of ground granulated blast-furnace slag as clinker replacement is becoming increasingly popular. Although the effects of this addition in the properties of cementitious materials are influenced by their hardening conditions, there are not too many experimental studies in which slag concretes have been exposed to real in situ environments. Then, the main objective of this research is to study the short-term effects of exposure to real Mediterranean climate environment of an urban site, where the action of airborne chlorides from sea water and the presence of CO2 are combined, in the microstructure and service properties of a commercial slag cement concrete, compared to ordinary Portland cement (OPC). The microstructure was studied with mercury intrusion porosimetry. The effective porosity, capillary suction coefficient, chloride migration coefficient, carbonation front depth, and compressive strength were also analyzed. Considering the results obtained, slag concretes exposed to a real in situ Mediterranean climate environment show good service properties in the short-term (180 days), in comparison with OPC.

Impedance Spectroscopy Study of the Effect of Environmental Conditions on the Microstructure Development of Sustainable Fly Ash Cement Mortars

Today, the characterisation of the microstructure of cement-based materials using non-destructive techniques has become an important topic of study, and among them, the impedance spectroscopy has recently experienced great progress. In this research, mortars with two different contents of fly ash were exposed to four different constant temperature and relative humidity environments during a 180-day period. The evolution of their microstructure was studied using impedance spectroscopy, whose results were contrasted with mercury intrusion porosimetry. The hardening environment has an influence on the microstructure of fly ash cement mortars. On one hand, the impedance resistances R1 and R2 are more influenced by the drying of the materials than by microstructure development, so they are not suitable for following the evolution of the porous network under non-optimum conditions. On the other hand, the impedance spectroscopy capacitances C1 and C2 allow studying the microstructure development of fly ash cement mortars exposed to those conditions, and their results are in accordance with mercury intrusion porosimetry ones. Finally, it has been observed that the combined analysis of the abovementioned capacitances could be very useful for studying shrinkage processes in cement-based materials kept in low relative humidity environments.

Steel Corrosion Rate Measurements in FA Concrete Using Three Electrochemical Techniques

Blended cements are today commonly used for concrete structures built near the sea. When reinforced concrete is exposed to the atmospheric marine environment, it is necessary to consider steel corrosion caused by both, chloride ions and carbon dioxide. In this research, reinforced OPC and FA cement concrete samples have been tested in order to evaluate their comparative performance when exposed to chlorides, to CO2 and to both agents acting together. The techniques used to evaluate the steel corrosion rates have been the polarization resistance, intersection method of polarization curves, and electrochemical impedance spectroscopy. The results indicate a similar behavior of FA and OPC concrete for samples exposed to CO2. For the pure chloride exposure and the combined exposure regimes, the behavior depends on the type of binder. The polarization resistance technique appears to show some limitations when there is not enough electrolyte inside the pores.

Properties of Concrete Paving Blocks and Hollow Tiles with Recycled Aggregate from Construction and Demolition Wastes

In recent years there has been an increasing tendency to recycle the wastes generated by building companies in the construction industry, demolition wastes being the most important in terms of volume. The aim of this work is to study the possibility of using recycled aggregates from construction and demolition wastes in the preparation of precast non-structural concretes. To that purpose, two different percentages (15% and 30%) of natural aggregates were substituted by recycled aggregates in the manufacture of paving blocks and hollow tiles. Dosages used by the company have not been changed by the introduction of recycled aggregate. Precast elements have been tested by means of compressive and flexural strength, water absorption, density, abrasion, and slipping resistance. The results obtained show the possibility of using these wastes at an industrial scale, satisfying the requirements of the Spanish standards for these elements.

The importance of urban sustainable development in a flood threatened area: the case of the northern coast of El Campello (Spain)

The southeast coast of the Iberian Peninsula (Spain and Portugal), and especially the Costa Blanca, is a very important tourist destination. Tourism has produced intense urban development, and in most cases, buildings and urban zones have occupied an important part of ravine basins. One of the most important climate features of this geographic area is a very intense and localized rainfall. As a consequence of these rainfalls, water levels in ravines are high. In this work, in order to study the relationship between unsustainable urban development and flood threats, a coastal zone situated in the northern coast of El Campello (Alicante province, Spain) was chosen. Eight ravines flow into the Mediterranean Sea in this area. For each ravine, turnoff thresholds and water levels estimation were calculated for two situations: the first one is the present situation and the second one is a hypothetical initial situation, before the touristic development without urban zones in these basins. Finally, there is a high decrease of turnoff thresholds and a rise of water levels in the studied basins. Then, it could be concluded that an unsustainable urban development produces an increase of flood threat in the particular case of the Costa Blanca, and in general in the southeast coast of Spain, due to their geographic and climate features.