Analysis of stray current induced by cathodic protection on steel-framed masonry structures

Cathodic protection (CP) has been successfully employed to protect steel-framed masonry buildings from corrosion related damage. When a CP system is installed to protect the structural members, other metallic items which are within the fabric of the structure but are not in direct electrical continuity may suffer from stray current interactions, resulting in accelerated corrosion of the discontinuous items. Therefore, these must be considered when CP systems are designed prior to installation. This paper presents both experimental and numerical studies into the risk and extent of stray current corrosion in steel-framed masonry structures when subject to impressed current cathodic protection. The objective is to allow CP systems to be optimised so that interference is minimised without compromising the technical or cost benefits of this method of corrosion control

Pore size distribution of an alkali activated cementitious (AACM) mortar

This paper reports an investigation on the size and distribution of capillary and gel pores in an alkali activated cementitious (AACM) mortar and comparative OPC mortar. These pore properties were determined from the cumulative and differential pore volume curves obtained by mercury intrusion porosimetry (MIP). The classification and distribution of these pores provides a useful insight to the properties of hardened concrete such as the durability, fire resistance and mechanical properties. The results show that AACM mortar mixes possess a bimodial pore size distribution while OPC concrete has unimodial pore sizes distribution. The intrudable porosity is lesser in AACM mortar than OPC mortar. The volume of the capillary pores was higher in AACM mortar compared with OPC mortar. However, the volume of the gel pores was much lower in AACM mortar than OPC mortar. The distribution of bimodal pores in AACM mortar is greatly influenced by the effects of curing type and the activator dilution. The distribution of unimodal pores in OPC mortar is similarly influenced by the curing type

Characterization and pore structure of rice husk ash cementitious material

An Investigation on the mineralogical and chemical characterization, pore structure, chemical shrinkage and pozzolanic activity of commercially produced rice husk ashes (RHA 1 and 2) and a control silica fume (SF) are presented in this paper. RHA possesses high silica content like silica fume which is used as supplementary cementitious materials (SCM) in the production of concrete. There is a need for an alternative to silica fume in the production of concrete because of its high demand and relatively high cost. The mineralogical composition of RHA 1 and 2 show high silica content of 77% and 84% respectively which is close to the silica content (˃80%) of class 2 silica fume. The oxides of Ca are 3.53% and 7.68% while Al is 1.19% and 1.29% for RHA 1 and 2 respectively which suggest that RHA is a low Ca+2 content binder. The results of chemical shrinkage of RHA 1, 2 and SF are 0.42 mL/g, 0.52 mL/g and 0.11 mL/g after 500 hrs of hydration. This indicates that RHA 2 has the highest reactivity (hydration) with water due to its highest Ca+2 content

Bound chloride ingress in alkali activated concrete

Alkali activated cementitious material (AACM) concrete and conventional concrete specimens of similar strength, developed for structural applications, were exposed to a 5% NaCl solution. Bound chloride concentrations (water and acid soluble) were determined up to 270 days of chloride exposure. Chloride diffusion profiles with depth and diffusion parameters C0 and Dc were derived from the data for water soluble, acid soluble and total bound chloride concentrations in order to develop long term chloride prediction relationships. The results show that the practice of using acid soluble chloride data for long term chloride predictions in conventional concrete is not valid for AACMs due to their low chemical binding capacity. Instead the physically bound chloride (water soluble) is more predominant in AACMs and is suitable for the chloride prediction models. Therefore, relationships of chloride diffusion parameters C0 and Dc with time have been derived for water soluble chloride. These correlate with total bound chlorides and are suitable for long term predictions of chloride concentrations for the design and maintenance of AACM concrete structures against corrosion

Influence of shear reinforcement corrosion on the performance of under-reinforced concrete beams

The in-service performance of reinforced concrete beams can be severely affected through cor-rosion of the steel reinforcement when it becomes subjected to harsh corrosive environments containing chlo-rides and carbon dioxide. In such instances, corrosion is likely to occur in the steel reinforcement, with the expansive nature of the corrosion products likely to induce cracking and spalling of the concrete. A loss of structural integrity (stiffness) will occur and this can severely influence the serviceability of the member. The purpose of this paper is to investigate the relationship between degree of corrosion and loss of stiffness in corrosion damaged under-reinforced concrete beams. Beams (100mm x 150mm cross section) were subjected to accelerated corrosion in the laboratory and subsequently tested in flexure to failure. The paper reports on the results of these tests and relates the degree of corrosion in the main steel to the percentage loss in stiffness in the concrete beams

Efficacy of different materials and methods of repair in highway bridges

Repairs were carried out on three highway bridges using repair materials of higher elastic modulus than the substrate, Erm>Esub and materials with ErmEsub perform efficiently. Hand applied repairs act as cosmetic repairs with no significant load transfer. Application of repair to propped structures leads to unpredictable stress redistribution in the long-term

Microwave curing parameters of in-situ concrete repairs

Different proprietary repair materials and a CEM II mortar were used to characterise the relationship between the main parameters of microwave curing (power, curing time, temperature rise and volume). The time-temperature-power relationships are linear for normal, non-rapid setting repair materials cured within the recommended temperature range taking account of temperature variation and heat of hydration. A general relationship between the microwave curing parameters of power, temperature rise, curing time and repair volume has been derived. It has been used to design and operate a prototype system. Steel reinforcement in the repair remains free from arcing under microwave exposure

Temperature development in microwave cured repair materials

This paper is part of the FP7 MCure project on the development and demonstration of an energy efficient system for accelerated curing during repair of concrete structures. It provides laboratory results on temperature development in microwave cured specimens of six commercial repair materials and a CEM II mortar. Specimens were cast in 100 mm polystyrene moulds and exposed to 60 Watts microwave power to reach approximately 40 °C recommended temperature for microwave curing. Temperature development of specimens was monitored for 24 hours after mixing. The results show that microwave curing triggers the peak heat of hydration and brings it forward for all repair materials. In addition, internal temperatures of specimens are higher than the top surface temperatures and the difference increases with increasing temperature. These laboratory based results are backed by the currently confidential data obtained from pre-industry prototype tests which are being used to upgrade the technology to industrial scale

Microwave curing of concrete bridge repairs

The paper introduces the FP7 MCure project on the "Development and demonstration of an energy efficient system for accelerated curing during repair and refurbishment of concrete structures". It provides test results on microwave curing of six commercial repair materials. The results provide the basic relationships between microwave energy input and curing characteristics of the repair materials by presenting data on the following aspects: • Surface temperature profiles and hot spots. • Interrelationships between temperature profiles, power input, volume and microwave curing time for different repair materials. • Response of different repair materials to microwave power. • Recommendations on optimum curing temperatures and curing time.</p