CSA Corrosion Abstracts

Every year, colossal amounts of used and non-biodegradable rubber tyres are accumulated in the world. Experience shows that the most efficient way to increase the concrete fracture energy GF (N/m) is to use metal or polypropylene fibres. The optimal content of fibre increases concrete resistance to stress (especially tensile stress under bending force). Concrete fracture is not brittle; concrete continues deforming after maximum stresses and is able to resist certain stresses, there is no abrupt decrease in loading. The research has proved that crumb rubber can be used in concretes as an alternative to metal and polypropylene fibres. The investigation has found that rubber waste additives, through their specific properties can partly take up tensile stresses in concrete and make the concrete fracture more plastic; besides, such concrete requires a significantly higher fracture energy and concrete samples can withstand much higher residual strength at 500 mm crack mouth opening displacement (CMOD) and deflection.

Experimental tests have determined the effect of slag, opoka (silica-calcite sedimentary rock), silica fume (SiO2) suspension, dolomite dust and sodium silicate solution (NaSS) together with the polycarboxylatether based plasticizing admixture on the yield stress and viscosity of Portland cement paste the rheological properties of which have been defined applying a rotational viscometer with co-axial cylinders. The tests have revealed that slag, opoka, silica fume suspension and dolomite dust added to cement paste by replacing 10% of Portland cement (by weight) have an effect on the yield stress and viscosity of the paste subject to the form and fineness of additive particles. When 10wt% of Portland cement is replaced with slag cement, the yield stress of Portland cement paste reduces by about 25.9%, and viscosity increases by about 3.5 times compared with the yield stress and viscosity of reference cement paste. The yield stress of Portland cement paste with 0.5% NaSS admixture increases insignificantly, and viscosity grows approximately twice compared with reference cement paste. The tests have also showed that the modifying admixtures of Portland cement paste enable to control the rheological properties of cement paste.

The paper considers the velocities of air movement in the ventilated air gaps of walls and focuses on pressure fields in both wall models arranged in a climatic chamber and exploited houses. The article investigates the influence of air movement on heat transfer through walls applying numerical modelling methods and conducting experiments in the climatic chamber. The thermal effects of air flows have been described with reference to the Nusselt number defined as the ratio of average convective and conductive heat fluxes and heat flux through still air.

Numerous alternatives exist for foundation systems and construction technologies. The systems can be described by different criteria values which are incorporated in the conventional design process. Decision on the most suitable construction technology is vital for success and depends on many effectiveness criteria. The business success depends on the right choice. The mandate of a construction management researcher is to use rational, systematic, science-based techniques to inform and improve various decisions. The paper presents multiple criteria decision making model for selection of a pile-column technology. The technological criteria are determined by an experimental study. Based on in-situ investigation of natural soil conditions, criteria values are determined. The decision making model incorporates five different methods and techniques. To solve a problem, it uses three multiple criteria decision making methods. Integrated criteria weights are determined by using the analytic hierarchy process and the expert judgement method. This model could be used to solve complicated problems pertaining to the selection of a construction technology.

Widely developed DH systems in Lithuanian towns and small settlements undergo modernisations aimed to increase their efficiency and heat supply quality. Typically, modernisations include the replacement of building heat substations, the reduction of heat losses in pipes and more efficient heat production, including the use of indigenous fuel resources. It was notified that new heat substations equipped with automatic heating control devices have backward impact on the technological parameters of DH networks. Modelling tools for simulation of hydraulic and thermal parameters in the network allow estimating of potential deviation of heat carrier temperature with loading variations not only during the season of the year, but also over day and night. Special technical measures can be taken to avoid unduly low heat carrier supply temperatures and violation of hot water supply quality requirements. Cost estimation of such measures versus the option of full network renovation is presented in the article.

The study examins risk factors of fatal vs serious injuries of construction workers’ fall from height. Fatal injury falls were matched against serious injury falls, and descriptive analyses were carried out according to investigation reports. Fatal injuries occurred predominantly because of the ignorance of passive personal protective equipment. In contrast, serious injuries predominantly occurred for ergonomic reasons during 1999–2002, and during period 1991–1998 safety measures.

Synthetic semi-hydrate gypsum (E-CaSO4×0.5H2O) is obtained during the phosphoric acid extraction from apatite process by sulphuric acid and its moisture content reaches ~30 %. This technogenic product due to its low activity and contamination by acidic mineral admixtures cannot be used for producing construction materials. It is very important from an economical and environmental point of view to utilise one of the most massive by-products because about 1 million tons goes to fill up landfills. The possibilities of using this by-product is investigated in this paper. Waste dehydration and drying process control was enacted by using the X-ray analysis method with an X-ray diffractometer DRON-1 and investigating the initial and the dried phosphogypsum product mineral composition. A rotary crusher IPR M-1 was used to pulverise the hydrated phosphogypsum before drying. The phosphogypsum mechanical activation was performed by a disintegrator DIA-01. As it can be seen from the obtained results, extractive semi-hydrate phosphogypsum can be reprocessed into building G4 grade gypsum. An operative PG delivery and collection system for roentgenographic mineral composition analysis was prepared and tested, which allowed to optimise and control the dehydration process. A gypsum cement composition was selected (70 % extractive semi-hydrate phosphogypsum, 20 % portlandcement, 10 % microsilica) which allowed to obtain a binding material with a density of > 1600 kg/m3 and compressive strength of ~ 33 MPa.

The paper aims to determine the effect of lime/Portland cement ratio in the matrix and basalt wool additive in porous concrete formation mixes on the macro- and microstructure, strength and frost resistance of specimens subjected to volumetric and one-side freezing and thawing. It has been found that porous concrete specimens with lime/Portland cement ratio of 1:1 (according to the equivalent amounts) subjected to volumetric freezing and thawing meet frost resistance standards (for concrete of the grade F 25). Mass losses of specimens with the addition of 0,4 % of basalt fibres made as little as 2% after 25 freeze-thaw cycles, while their compression strength increased. Light-weight porous concrete articles should not be used for one-sided freezing-thawing method. The effect of fibre additives on the micro- and macrostructure is negligible.

An effect of service and proof actions on probabilistic reliability (serviceability, safety and durability) of building elements (components and members) of existing enclosure and bearing structures is under consideration. Time-dependent models for reliability assessment of elements under sustained variable and multicycle actions are presented. Revised reliability indices of existing elements exposed to service permanent and variable actions are discussed. It is recommended to assess the long-term reliability index of elements taking into account the effect of latent defects. Truncated probability distributions of physical-mechanical resistances of elements and an effect of their latent defects on reliability index assessment are taken into account. Methodological peculiarities of durability prediction of elements and avoiding unfounded premature repairs or replacements are analysed. The applied illustration of the presented method on the probabilistic reliability prediction of deteriorating concrete covers is demonstrated.

Remiantis eksperimentinio tyrimo rezultatais, pasiūlyta patikslinti medžiagų sąlyčio zonoje vykstančių drėgminių procesų matematinį modelį. Kapiliariniam įgėriui silpnėjant, prasideda kitas sąlyčio zonos drėgminio būvio etapas – kondensato „išspaudimas“ į šiltinamąją medžiagą ir galimas jo judėjimas dėl gravitacijos. Didinant apšiltinimo efektyvumą iš esmės keičiasi drėgmės perdavimo mechanizmas.