Investigation on the effect of supplementary cementitious materials on the critical chloride threshold of steel in concrete

open3noThe critical chloride threshold is a key parameter in the service life design of reinforced concrete structures exposed to chloride-bearing environments. This paper investigates the role of concrete composition, and particularly the effect of supplementary cementing materials, on the chloride threshold. To simulate real exposure conditions, ponding tests were carried out on reinforced concrete specimens with bars in free corrosion conditions and corrosion initiation was detected through corrosion potential and corrosion rate measurements. After two and a half years, the ponding was followed by an ageing period and the initiation of corrosion was further detected with anodic potentiostatic polarisation tests. Results of the tests showed several limitations of the approach based on chloride penetration and monitoring of free corrosion parameters to investigate the chloride threshold. In spite of this, a possible role of natural pozzolan and coal fly ash additions in leading to higher values of the chloride threshold and ground limestone in promoting lower values of the chloride threshold could be observed.Lollini, Federica; Redaelli, Elena; Bertolini, LucaLollini, Federica; Redaelli, Elena; Bertolini, Luc

A study on the cement-based decorative materials in the San Fedele Church in Milan

Cement-based materials have been used since the 19th century for different decorative purposes, and a high levels of expertise has often reached in reproducing or restoring even quite elaborated stoneworks. An important example is the application of cement-based decorative materials on the façades of the San Fedele church in Milan. The church, built in the 16th century and characterized by the presence of pinkish-yellowish Angera stone on the façades, was subjected, especially in the 20th century, to several restoration works. Damaged decorative elements of the façades as well as portions of its structural elements were replaced or covered in the last century by â\u80\u9cstone imitating renderâ\u80\u9d, made with cementitious materials which imitate the original Angera stone. In this study, several samples of cement-based decorative materials, collected from different elements of the external façades of the Church, were characterized by several analytic techniques (thermogravimetric analysis, X-ray diffraction, scanning electron microscopy and IR analysis), in order to investigate both their microstructure and composition, how the chromatic aspect of the cementitious materials were obtained and their conservation state and to provide useful information for the possible reproduction of materials with comparable appearance to be used in a further restoration project. Results showed that the cement-based materials and decorations were obtained by the application of different layers of renders; in particular, the colour and texture of finishing layer were achieved by blending the binder with fine dolomite particles, probably obtained by grinding the Angera stone. This technique not only allowed an amazing reproduction of the original stone, but also resulted in a durable protection, since the cement-based decorative materials did not show any significant degradation phenomena in the polluted environment of the centre of Milan

Cathodic protection with localised galvanic anodes in slender carbonated concrete elements

A combined experimental and numerical investigation was carried out with the aim of determining whether few localised galvanic anodes per unit length could protect the reinforcement of slender carbonated concrete elements, exposed to atmospheric conditions, which could not be repaired with traditional methods. Initially, the cathodic behaviour of steel under galvanostatic polarisation was determined on small-size specimens obtained from a real element. A correlation of potential versus applied current was obtained. The current distribution in slender elements was then determined through finite elements simulations, considering various scenarios of carbonation and humidity. Results showed that, in spite of the high electrical resistivity of carbonated concrete, anodes with spacing of 0.45 m are enough to protect corroding reinforcement in most exposure conditions, even in thin parts of element. Estimated anode durations were of the order of several years or even decades; however, it was shown that also reinforcement in dry (carbonated or alkaline) concrete, which does not need to be protected, contributes to anode consumption. Although other aspects play a role on the performance of a cathodic protection system (such as the effectiveness of anode-encasing material and of electrical connection to reinforcement), the results obtained are supportive of a repair strategy based on the use of localised galvanic anodes and can be generalised to slender elements exposed to atmospheric conditions suffering carbonation induced corrosion

Effects of nanosilica on compressive strength and durability properties of concrete with different water to binder ratios

The effects of the addition of different nanosilica dosages (0.5%, 1%, and 1.5% with respect to cement) on compressive strength and durability properties of concrete with water/binder ratios 0.65, 0.55, and 0.5 were investigated. Water sorptivity, apparent chloride diffusion coefficient, electrical resistivity, and carbonation coefficient of concrete were measured. The results showed that compressive strength significantly improved in case of water/binder = 0.65, while for water/binder = 0.5 no change was found. Increasing nanosilica content, the water sorptivity decreased only for water/binder = 0.55. The addition of 0.5% nanosilica decreased the apparent chloride diffusion coefficient for water/binder = 0.65 and 0.55; however, higher nanosilica dosages did not decrease it with respect to reference value. The resistivity was elevated by 0.5% nanosilica for all water/binder ratios and by 1.5% nanosilica only for water/binder = 0.5. The carbonation coefficient was not notably affected by increasing nanosilica dosages and even adverse effect was observed for water/binder = 0.65. Further information of microstructure was also provided through characterization techniques such as X-ray diffraction, thermal gravimetric analysis, mercury intrusion porosimetry, and scanning electron microscopy. The effectiveness of a certain nanosilica dosage addition into lower strength mixes was more noticeable, while, for the higher strength mix, the effectiveness was less

Extent of corrosion damage for RC structures exposed to chloride-bearing environment

In industrialized countries, most of the reinforced concrete (RC) structures and infrastructures have more than 40 years, since they were built around 1960 − 1980, and were designed for a service life of 50 years. Consequently, in the next years, the number of structures and infrastructuresthat will need to be repaired will steeply increase. Several techniques, characterized by a different durability, environmental impact and economic impact, are available for the repair of a reinforced concrete structure damaged by the corrosion of reinforcement. To help the designers in the choice of the most suitable one, a preliminary assessment of the condition of the structure is essential, aimed at diagnosing the causes of deterioration, the extent of damage, i.e. the extent of corroding reinforcement, and its evolution in time. An approach, with a wide consensus, for the evaluation of the extent of corroding reinforcement is available for carbonation-induced corrosion, whilst it is still lacking forchloride-induced corrosion. In this paper two approaches for the evaluation of the extent of corroding reinforcement for a RC structure subject to chloride-induced corrosion are presented and compared, showing similar results. These approaches can be useful to properly plan a restoration intervention as well as to assess the reliability of the recently proposed model for service life design

The Promise of Preventive Cancer Vaccines

Years of unsuccessful attempts at fighting established tumors with vaccines have taught us all that they are only able to truly impact patient survival when used in a preventive setting, as would normally be the case for traditional vaccines against infectious diseases. While true primary cancer prevention is still but a long-term goal, secondary and tertiary prevention are already in the clinic and providing encouraging results. A combination of immunopreventive cancer strategies and recently approved checkpoint inhibitors is a further promise of forthcoming successful cancer disease control, but prevention will require a considerable reduction of currently reported toxicities. These considerations summed with the increased understanding of tumor antigens allow space for an optimistic view of the future

Vaccines against human HER2 prevent mammary carcinoma in mice transgenic for human HER2

INTRODUCTION: The availability of mice transgenic for the human HER2 gene (huHER2) and prone to the development of HER2-driven mammary carcinogenesis (referred to as FVB-huHER2 mice) prompted us to study active immunopreventive strategies targeting the human HER2 molecule in a tolerant host. METHODS: FVB-huHER2 were vaccinated with either IL-12-adjuvanted human HER2-positive cancer cells or DNA vaccine carrying chimeric human-rat HER2 sequences. Onset and number of mammary tumors were recorded to evaluate vaccine potency. Mice sera were collected and passively transferred to xenograft-bearing mice to assess their antitumor efficacy. RESULTS: Both cell and DNA vaccines significantly delayed tumor onset, leading to about 65% tumor-free mice at 70 weeks, whereas mock-vaccinated FVB-huHER2 controls developed mammary tumors at a median age of 45 weeks. In the DNA vaccinated group, 65% of mice were still tumor-free at about 90 weeks of age. The number of mammary tumors per mouse was also significantly reduced in vaccinated mice. Vaccines broke the immunological tolerance to the huHER2 transgene, inducing both humoral and cytokine responses. The DNA vaccine mainly induced a high and sustained level of anti-huHER2 antibodies, the cell vaccine also elicited interferon (IFN)-gamma production. Sera of DNA-vaccinated mice transferred to xenograft-carrying mice significantly inhibited the growth of human HER2-positive cancer cells. CONCLUSIONS: Anti-huHER2 antibodies elicited in the tolerant host exert antitumoral activity

Impact of RAP as recycled aggregate on durability-related parameters of structural concrete

In view of promoting the recycling of construction and demolition waste, the re-utilization of Recycled Asphalt Pavement (RAP) as aggregate in structural concrete has been recently proposed and investigated. Although many studies are available on the physical and mechanical characterisation of concrete containing RAP, little is still known about how medium- to long-term durability performances are affected by the partial or total replacement of natural aggregates with RAP aggregate. In this experimental study, several durability-related properties were assessed, with the aim of investigating the possible use of RAP as partial or total replacement of natural aggregates for reinforced concrete applications. In particular, concretes were obtained with increasing RAP contents (from reference mixtures with natural aggregate only, to complete substitution with RAP aggregate), two different cement types (Portland-limestone and pozzolanic), and two water/cement ratios (0.45 and 0.65), representative of two exposure classes for chloride and carbonation induced corrosion. Water sorptivity through capillary suction and water absorption were investigated, together with the resistance to the penetration of carbonation, both under accelerated and natural exposure, and the resistance to the penetration of chlorides, under natural diffusion. Relationships between physical and mechanical properties, such as total open porosity and compressive strength, and durability-related properties were also investigated. Results showed that sorptivity experienced a neat decrease for increasing RAP contents, due to the hydrophobic nature of RAP aggregate, while water absorption was less affected. Resistance to the penetration of carbonation and chlorides were both more clearly affected by other mix design variables, such as w/c ratio and cement type, rather than RAP content

Corrosion of Steel in Concrete and Its Prevention in Aggressive Chloride-Bearing Environments

This keynote paper deals with the durability of reinforced concrete (RC) structures exposed to aggressive environments characterized by high concentration of chloride ions, namely, marine environments or the use of de-icing salts. The mechanism of chloride-induced corrosion of steel in concrete is introduced, and its influence on the service life of RC structures is analyzed. Factors affecting the time to corrosion initiation are described with regard to both concrete properties and environmental exposure conditions. Design approaches available for achieving durability targets associated with the design service life are analyzed, focusing on studies carried out by the authors in recent years at the mCD Concrete Durability lab of Politecnico di Milano, which were aimed at improving the protection provided to the steel bars by the concrete cover, investigating the advantages of using corrosion-resistant stainless steel bars and developing the electrochemical technique of cathodic prevention