Investigating Effects of Metakaolin Content on the Physical Properties of Concrete, and its Susceptibility to Colonization and Biodegradation by Sulphur Oxidizing Bacteria

Biogenic sulphuric acid attack on concrete is a concern worldwide, as it can lead to collapse of sewer infrastructure. Despite knowledge of the cause and the degradation pathways, not much is known about colonization patterns by sulphur oxidizing bacteria. These bacteria were grown on concrete in attempts to catalog degradation and colonization patterns. This was achieved using a battery of concrete property tests and experimenting with imaging techniques. Increased metakaolin content of concrete decreased sorptivity and chloride permeability of concrete while increasing strength and porosity. Concrete with higher metakaolin appeared more resistant to biogenic acid attack, despite increased porosity. Advances were made in protocols for imaging bacteria on a concrete surface, a challenge given the presence of autofluorescing materials in concrete. Information gained has shown that imaging bacteria on an autofluorescent surface can be achieved, and recommendations are made to further advance these efforts.

Investigating Effects of Metakaolin Content on the Physical Properties of Concrete, and its Susceptibility to Colonization and Biodegradation by Sulphur Oxidizing Bacteria

Biogenic sulphuric acid attack on concrete is a concern worldwide, as it can lead to collapse of sewer infrastructure. Despite knowledge of the cause and the degradation pathways, not much is known about colonization patterns by sulphur oxidizing bacteria. These bacteria were grown on concrete in attempts to catalog degradation and colonization patterns. This was achieved using a battery of concrete property tests and experimenting with imaging techniques. Increased metakaolin content of concrete decreased sorptivity and chloride permeability of concrete while increasing strength and porosity. Concrete with higher metakaolin appeared more resistant to biogenic acid attack, despite increased porosity. Advances were made in protocols for imaging bacteria on a concrete surface, a challenge given the presence of autofluorescing materials in concrete. Information gained has shown that imaging bacteria on an autofluorescent surface can be achieved, and recommendations are made to further advance these efforts.

The tensile strength: The most fundamental mechanical characteristics of concrete

Concrete is an inhomogeneous building material. It has a considerable and reliable compressive strength and a relative low tensile strength which can be even exhausted locally under unfortunate conditions. It is quite obvious that the concrete tensile strength was always reprehended as the most unreliable concrete property. A simple relationship between tensile- and compressive strength is introduced. The mechanical background of the relation tensile- to compressive strength in case of ‘normal’ and high strength concretes is elucidated. Mechanical bond, too, relies completely on the tensile strength. In the design of structural concrete members the tension fields are more characteristic than the compression fields. Effective concrete strengths are not successful. Tensile strength can be applied as ‘yield condition’ for the lower bound solution in the theory of plasticity. The paper intends to contribute to the acceptance of the tensile strength as the more fundamental concrete characteristics.

Internet User: the Concept and Types

The article discusses the concepts and types of Internet users. Using technical and legal means, a personal definition of an Internet user is proposed. By the term «Internet user» we propose to understand — a participant of Internet relations (both a natural and a legal entity) who uses capabilities of information environment to satisfy his/her personal needs in sale of goods, works and services. The researcher notes that in national legislation of Ukraine there is no legal regulation of the concept and types of Internet users. The study analyzed and formulated types of Internet users. The Internet user, as a participant in various Internet relations, is marked by special features due to the nature of such relations. A specific composition of Internet users who take part in such relations was identified depending on dedicated types of Internet relations. Their brief characteristic is provided. At the same time, legal status of Internet user is compared with the consumer. On the whole, current legislation is not a perfect means of legal influence on internet relations which are connected with Internet user, and requires its timely improvement. It was proposed to supplement provisions of Law of Ukraine «On the protection of consumer rights» with provisions that extend legal status to Internet user which consumer has in its traditional sense (i.e. the concept, rights, obligations, procedure of judicial protection, liability for violation the legislation about protection of Internet users’ rights). The concept of Internet user fully reflects characteristics of a participant in civil law relations. This is especially clearly emphasized by analysis of its types and ratio with consumer category. The Internet user is endowed with a wide range of «traditional» rights and obligations of a participant in civil law relations, which are enshrined in national and international legislation. The Internet user acquires concrete property and personal non-property rights and corresponding duties that determine its civil and legal status.

Rice Husk Ash as Fine Aggregate Sustainable Material for Strength Enhancement of Conventional and Self Compacting Concrete

Rice husk ash (RHA) is a by-product of the rice milling industry. Near about 20 million tonnes of RHA is produced annually which creates environmental pollution. Utilization of RHA as a supplementary cementitious material adds sustainability to concrete by reducing CO2 emission of cement production. But, the percentage of utilization of RHA is very less. This paper presents the results of an experimental investigation to study the effects of partial replacement of fine aggregate with RHA on mechanical properties of conventional and self-compacting concrete (SCC). The fine aggregate is replaced by RHA in conventional concrete (CC) with six different percentage by weight such as 0%, 10%, 20%, 30%, 40% and 50% having w/c ratio 0.375 with variation of super plasticiser dose, whereas in SCC the replacement of fine aggregate by RHA is 0%, 10%, 20%, 30%, 40%. The design mix for CC is targeted for M30 grade concrete. The fresh concrete test of SCC is conducted by using slump flow, T500, J-ring, L-box, U-box and V-funnel to know the filling ability, flow ability and passing ability of SCC. As fresh concrete property concerned, the result indicates that the slump flow value satisfied the EFNARC 2005 guidelines upto 30% replacement of fine aggregate with RHA whereas 40% replacement did not satisfy the guideline. As hardened concrete property concerned, the compressive strength, split-tensile strength and flexural strength of CC and SCC are determined at 7, 28 and 90 days. The test result indicates that upto 30% replacement of fine aggregate with RHA enhances the strength in CC whereas the strength enhancement in SCC upto 20% replacement.