Measurement and characterisation of concrete substrate roughness in patch repairs

Patch repair is one of the most common types of repair in reinforced concrete bridges. The overall success and long-term durability of a patch repair is significantly influenced by the bond developed at the interface between the concrete substrate and the repair material. In turn, the bond strength is influenced by the topography (roughness) of the substrate surface after removal of the defective concrete. However, different removal methods of defective concrete produce substrate surfaces with different topographies. Hence, the ability to measure and characterise the topography of substrate surfaces is of great importance for evaluating the effectiveness of different removal methods. In this paper the effect of two removal methods: electric chipping hammers and Remote Robotic Hydro-erosion (RRH) on the surface roughness is investigated. The paper also presents an alternative to current BS EN 1504-10 surface roughness measurement methods (sand patch and contact stylus profilometry), which overcomes some of their limitations. It employs state of the art fringe-based laser interferometry which provides a more accurate measurement and characterisation of concrete substrate surfaces. In addition, it has the potential for use in other fields of concrete bridge maintenance and rehabilitation where surface roughness is important such as FRP laminate strengthening and application of water proof coatings

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 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

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

Η επίδραση της εμφύσησης οξυγόνου στον αερισμό τραχειοστομημένων ασθενών της ΜΕΘ κατά την αποδέσμευση από τον αναπνευστήρα

Η έρευνα πραγματοποιήθηκε σε ενήλικες τραχειοστομημένους ασθενείς της ΜΕΘ, οι οποίοι εισήχθησαν στην μελέτη ως αιμοδυναμικά και αναπνευστικά σταθεροί κατά την δοκιμασία αποδέσμευσής τους από τον μηχανικό αερισμό. Όλοι οι ασθενείς διέθεταν παροχή οξυγόνου μέσω διάταξης T-piece και υποβάλλονταν σε παράλληλη εμφύσηση αναπνεόμενου μείγματος μέσω ενδοτραχειακού καθετήρα (TGI), όμοιας συγκέντρωσης (FiO2) και σταθερής ροής στα 6 ή στα 11 L/min, αλλά με τυχαία διαδοχή των πιο πάνω παροχών. Οι ασθενείς παρακολουθούνταν μέσω monitor και τομογράφου εμπέδησης καθ’ όλη τη διάρκεια της δοκιμασίας, κατά την οποία πραγματοποιούνταν μετρήσεις α) πριν την εφαρμογή της TGI, β) κατόπιν 15-λεπτης εφαρμογής της αρχικώς επιλεγμένης παροχής TGI, γ) κατόπιν 15-λεπτης εφαρμογής της δεύτερης κατά σειρά επιλεγμένης παροχής TGI και δ) 15min κατόπιν της επιστροφής του ασθενή στις προ-εφαρμογής TGI συνθήκες. Η εφαρμογή της τεχνικής έδειξε στατιστικά σημαντικές διαφορές στη συγκέντρωση του Οξυγόνου πριν την τοποθέτηση του ενδοτραχειακού καθετήρα (TGI στα 0 L/min) (105 ± 24.6 mmH2O) και μετά την επίδραση του TGI στα 6 και 11 L/min flow (115 ± 26.3 mmH2O and 127 ± 27 mmH2O αντίστοιχα) με p(6L/min)&lt;0.005 και p(11L/min)&lt;0,005. Επιπροσθέτως, έδειξε ελάττωση της αναπνευστικής συχνότητας μεταξύ των αρχικών τιμών (24.8 ± 6.7 b/sec), και των τιμών που κατεγράφησαν στα 11 L/min (20 ± 4.9 b/sec ) P(11L/min)=0.02, με παράλληλες αυξήσεις των λειτουργικών υπολειπόμενων όγκων παρατηρούμενων μέσω του τομογράφου εμπέδησης από τα 0 L/min στα 6L/min (ποσοστό αύξησης 1.46 ± 1.48 ) και από 0 L/min to 11 L/min (2.50 ± 1.73) με p(011L/min)&lt;0.05. Συμπερασματικά, αποδεικνύεται ότι η παράλληλη προσφορά αναπνευστικών αερίων μέσω TGI και T-piece προσφέρει αναπνευστική υποστήριξη στους τραχειοστομημένους ασθενείς της ΜΕΘ πιθανόν δε, να δρα ως επικουρικός παράγοντας για την παραμονή τους εκτός μηχανικού αερισμού άμεσα ή έμμεσα, ως ενδιάμεσο στάδιο προσαρμογής μεταξύ Τ-piece και αναπνευστήρα.Purpose: The tracheal insufflation of respiratory gases removes the exhaled carbon dioxide from the anatomical dead space of the lung. The present study intends to investigate the effect of the above phenomenon on specific respiratory parameters of patients breathing spontaneously via a tracheostomy tube. Materials/Methods: Eleven tracheostomized subjects, monitored by impedance tomography, supported by a T-piece device for covering their respiratory needs, were given supplementary oxygenation by a TGI catheter providing the same FiO2 in flows of 6 or 11L/min. Results: Oxygenation by a simple T-piece device compared to oxygenation by a combination of T-piece with supplemental TGI catheter delivering respiratory gases at flows of 6L/min and 11L/min, has statistical significant differences (p&lt;.05) in PaO2 (initial: 105±24.6mmHg, 6L/min: 115±26.3mmHg, 11L/min: 127±27mmHg), in breathing frequency (initial: 24.8±6.7, 11L/min: 20±4.9) and in End-tidal impedance variation (comparing TGI flow rates from 0 to 6L/min [1.46±1.48] and TGI flow rates from 0 to 11L/min [2.50±1.73], which corresponds to similar changes in FRC). Conclusions: Respiratory gases of the same FiO2, given by a combination of a Venturi type T-piece and a TGI catheter, to stable, tracheostomized, spontaneously breathing ICU patients, reduce the breathing frequency, increase the oxygen concentration in blood and the end-expiratory lung volume

Microwave system for in-situ curing of concrete repair

This paper presents some results of the FP7 MCure project on the development of a prototype system for microwave curing of concrete and concrete repair. Microwave curing of concrete provides higher early age strength compared to normally cured concrete. A prototype microwave curing system has been developed based on laboratory results on microwave curing of concrete repair materials. Subsequently, field trials were carried out to validate the Pre-Industrial Prototype system by testing elements of four commercial repair materials and a CEM II cement concrete. The prototype control system was used to record data such as surface temperature of concrete, moisture content of concrete and output power of the magnetron. In addition, the relationships between microwave output power, temperature and volume of repair of the field trials were derived and compared with the laboratory results. The prototype microwave system performed effectively. Slabs of dimensions 1 m x 1 m and depths up to 64 mm were microwave cured to temperature up to 45 ◦C for the predetermined time

Bond of steel reinforcement with microwave cured concrete repair mortars

This paper investigates the effect of microwave curing on the bond strength of steel reinforcement in concrete repair. Pull-out tests on plain mild steel reinforcement bars embedded in four repair materials in 100 mm cube specimens were performed to determine the interfacial bond strength. The porosity and pore structure of the matrix at the steel interface, which influence the bond strength, were also determined. Test results show that microwave curing significantly reduces the bond strength of plain steel reinforcement. The reduction relative to normally cured (20 °C, 60% RH) specimens is between 21 and 40% with low density repair materials and about 10% for normal density cementitious mortars. The corresponding compressive strength of the matrix also recorded similar reduction and microwave curing resulted in increased porosity at the interface transition zone of the steel reinforcement. A unique relationship exists between bond strength and both compressive strength and porosity of all matrix materials. Microwave curing reduced shrinkage but despite the wide variation in the shrinkage of the repair mortars, its effect on the bond strength was small. The paper provides clear correlations between the three parameters (compressive strength, bond strength and porosity), which are common to both the microwave and conventionally cured mortars. Therefore, bond-compressive strength relationships used in the design of reinforced concrete structures will be also valid for microwave cured elements

Hydration and microwave curing temperature interactions of repair mortars

Microwave curing of repair patches provides an energy efficient technique for rapid concrete repair. It has serious economic potential due to time and energy saving especially for repairs in cold weather which can cause work stoppages. However, the high temperatures resulting from the combination of microwave exposure and accelerated hydration of cementitious repair materials need to be investigated to prevent potential durability problems in concrete patch repairs. This paper investigates the time and magnitude of the peak hydration temperature during microwave curing (MC) of six cement based concrete repair materials and a CEM II mortar. Repair material specimens were microwave cured to a surface temperature of 40-45 °C while their internal and surface temperatures were monitored. Their internal temperature was further monitored up to 24 hours in order to determine the effect of microwave curing on the heat of hydration. The results show that a short period of early age microwave curing increases the hydration temperature and brings forward the peak heat of hydration time relative to the control specimens which are continuously exposed to ambient conditions (20 °C, 60% RH). The peak heat of hydration of normal density, rapid hardening Portland cement based repair materials with either pfa or polymer addition almost merges with the end of microwave curing period. Similarly, lightweight polymer modified repair materials also develop heat of hydration rapidly which almost merges with the end of microwave curing period. The peak heat of hydration of normal density ordinary Portland cement based repair materials, with and without polymer addition, occurs during the post microwave curing period. The sum of the microwave curing and heat of hydration temperatures can easily exceed the limit of about 70 °C in some materials at very early age, which can cause durability problems

Pore properties and moisture loss of repair mortars under low-impact microwave curing

Purpose Microwave curing (MC) can facilitate rapid concrete repair in cold climates without using conventional accelerated curing technologies which are environmentally unsustainable. Accelerated curing of concrete under MC can contribute to the decarbonisation of the environment and provide economies in construction in several ways such as reducing construction time, energy efficiency, lower cement content, lower carbonation risk and reducing emissions from equipment. Design/methodology/approach The paper investigates moisture loss and pore properties of six cement-based proprietary concrete repair materials subjected to MC. The impact of MC on these properties is critically important for its successful implementation in practice and current literature lacks this information. Specimens were microwave cured for 40–45 min to surface temperatures between 39.9 and 44.1 °C. The fast-setting repair material was microwave cured for 15 min to 40.7 °C. MC causes a higher water loss which shows the importance of preventing drying during MC and the following 24 h. Findings Portland cement-based normal density repair mortars, including materials incorporating pfa and polymer latex, benefit from the thermal effect of MC on hydration, resulting in up to 24% reduction in porosity relative to normal curing. Low density and flowing repair materials suffer an increase in porosity up to 16% due to MC. The moisture loss at the end of MC and after 24h is related to the mix water content and porosity, respectively. Originality/value The research on the application of MC for rapid repair of concrete is original. The research was funded by the European commission following a very rigorous and competitive review process which ensured its originality. Original data on the parameters of porosity and moisture loss under MC are provided for different generic cementitious repair materials which have not been studied before. Application of MC to concrete construction especially in cold climates will provide environmental, economic and energy benefits