Ignacio Segura

Bioreceptivity evaluation of cementitious materials designed to stimulate biological growth

Ordinary Portland cement (OPC), the most used binder in construction, presents some disadvantages in terms of pollution (CO2 emissions) and visual impact. For this reason, green roofs and façades have gain considerable attention in the last decade as a way to integrate nature in cities. These systems, however, suffer from high initial and maintenance costs. An alternative strategy to obtain green facades is the direct natural colonisation of the cementitious construction materials constituting the wall, a phenomenon governed by the bioreceptivity of such material. This work aims at assessing the suitability of magnesium phosphate cement (MPC) materials to allow a rapid natural colonisation taking carbonated OPC samples as a reference material. For that, the aggregate size, the w/c ratio and the amount of cement paste of mortars made of both binders were modified. The assessment of the different bioreceptivities was conducted by means of an accelerated algal fouling test. MPC samples exhibited a faster fouling compared to OPC samples, which could be mainly attributed to the lower pH of the MPC binder. In addition to the binder, the fouling rate was governed by the roughness and the porosity of the material. MPC mortar with moderate porosity and roughness appears to be the most feasible material to be used for the development of green concrete walls.

Evaluation of natural colonisation of cementitious materials: Effect of bioreceptivity and environmental conditions

Incorporation of living organisms, such as photosynthetic organisms, on the structure envelope has become a priority in the area of architecture and construction due to aesthetical, economic and ecological advantages. Important research efforts are made to achieve further improvements, such as for the development of cementitious materials with an enhanced bioreceptivity to stimulate biological growth. Previously, the study of the bioreceptivity of cementitious materials has been carried out mainly under laboratory conditions although field-scale experiments may present different results. This work aims at analysing the colonisation of cementitious materials with different levels of bioreceptivity by placing them in three different environmental conditions. Specimens did not present visual colonisation, which indicates that environmental conditions have a greater impact than intrinsic properties of the material at this stage. Therefore, it appears that in addition to an optimized bioreceptivity of the concrete (i.e., composition, porosity and roughness), extra measures are indispensable for a rapid development of biological growth on concrete surfaces. An analysis of the colonisation in terms of genus and quantity of the most representative microorganisms found on the specimens for each location was carried out and related to weather conditions, such as monthly average temperature and total precipitation, and air quality in terms of NOx, SO2, CO and O3. OPC-based specimens presented a higher colonisation regarding both biodiversity and quantity. However, results obtained in a previous experimental programme under laboratory conditions suggested a higher suitability of Magnesium Phosphate Cement-based (MPC-based) specimens for algal growth. Consequently, carefully considering the environment and the relationships between the different organisms present in an environment is vital for successfully using a cementitious material as a substrate for biological growth.

Sand-Cement Concrete in the Century-Old Camarasa Dam

Sand-cement emerged in the early twentieth century as an alternative binder in infrastructures that required a significant amount of concrete volume in order to reduce the costs associated with portland cement. This binder was first used in the United States in several dams before being applied in Camarasa Dam in Spain. Nearly a century after its construction, the dam exhibits degradation phenomena in the downstream face, manifested by losses of mass. The present study aims at assessing the state of the sand-cement concrete in Camarasa Dam and evaluate whether the degradation observed could affect the safety and functionality of the 95-year-old dam. For that, the state of the art on sand-cement is reviewed and an experimental program of physical, mechanical, and chemical tests is performed on samples from the dam. The results reveal that the degradation phenomena may be attributed to physical causes and a general degradation of the concrete properties is discarded as well as any effect on the safety and functionality of the dam.

Service-Life Assessment of Existing Precast Concrete Structure Exposed to Severe Marine Conditions

The overall performance of a concrete structure is considered to be a key issue when determining its service life. The widespread use of precast concrete and consideration of durability as a design parameter in most of the international codes have the goal of achieving concrete structures with better durability. Nevertheless, the early deterioration of concrete is still common in a large number of concrete structures, which reduces the service life. This paper presents a case study of an existing precast concrete cooling tower for a thermal power station subjected to severe marine exposure conditions, which showed symptoms of serious deterioration after operating for three years. The main goal of this study was to clarify the origin of the accelerated deterioration of the structure. Wetting-drying cycles were identified as the main cause of the early deterioration of the structure. Furthermore, estimations on its remaining service life were made considering the accelerating effect of the wetting-drying cycles. Finally, the variation in the safety factor of the main structural elements was evaluated.

Simplified Analytical Assessment of Damaged Induced by the External Sulphate Attack in Concrete Piles

Underground structures and foundations, including piles, constructed with reinforced concrete may be in contact with sulphate-rich soils and water. Structural elements exposed to these conditions may be affected by an expansive process known as external sulphate attack (ESA) that generally leads to an increase in volume, hence displacements and cracking of the concrete. The most widely accepted approach to mitigate such problems is to use cement(s) with a small content of aluminates. The objective of this research was to assess the potential damage induced by ESA using a simplified analytical model that is able to consider parameters such as the cement content and size of the pile, which may also affect the risk of damage. A parametric study was performed with different pile sizes and aluminate and cement contents. The structural integrity of the elements was verified considering a life span of 50 years and three possible failure modes (tensile failure in the core, and shear or tensile failure in the interface between the damaged and undamaged regions). The results suggest that the recommendations based solely on the maximum aluminate content present in the cement are inaccurate and might lead to very different outcomes depending on the characteristics of the elements. The study indicates that other parameters should also be taken into account in order to reduce the risk of ESA in real structures, such as the size of the element or the cement content per unit volume of concrete. This work has implications for the design of pile foundations in ground conditions prone to sulphate attack.