Static Hardness Testing of Cement Mortars Containing Different Types of Recycled Construction Waste Powders

The present paper deals with the hardness of cement mortars prepared with recycled materials that are potential supplementary cementitious materials (SCM). Two potential SCMs (aerated concrete powder (ACP) and concrete powder) were investigated and compared with a reference (neat cement) sample and a sample containing metakaolin (MK). The long-term performance of the mortars was studied up to the age of one year. Based on the compressive strength tests at different ages, neither concrete powder nor ACP significantly decreases the compressive strength at a 10% substitution ratio. The samples were studied with two types of static hardness tests: the Brinell hardness test and the depth sensing indentation test at two different load levels. The hardness test results indicated that the standard deviation of the results is lower at a higher load level. In the case of metakaolin and concrete powder, the change in the compressive strength was observable in the hardness test results. However, in case of the ACP, the compressive strength decreased, while the hardness increased, which can be traced back to the filler effect of aerated concrete powder. Finally, using the DSI test, the hardness results were analyzed on an energy basis. The analysis highlighted that the change in the hardness is connected to the elastic indentation energy, while it is independent from the dissipated (plastic) indentation energy.

Dynamic Hardness of MCrAlY Abradable Seal Coating

The purpose of this investigation is to study the dynamic hardness of MCrAlY abradable coatings under different strain rates. A dynamic indentation device based on the split Hopkinson pressure bar system (SHPB) was used. The results show that the hardness of MCrAlY coating increased with the increase of the strain rate, which has a positive strain rate effect. In addition, the difference of the static hardness of MCrAlY coating prepared by HVOF and LPPS was only 4%, while the difference in dynamic hardness was 16%.

The Effect of Heating Temperature on Static Hardness of Beech (Fagus Sylvatica L.) Wood

A study was carried out to evaluate the effects of heating treatment on static hardness of beech (Fagus sylvatica L.) wood of Albanian origin. The heat treatment was conducted at temperatures 180, 200 and 220°C for 2 hours, at atmospheric pressure. Samples were produced from logs sapwood of origin from central Albania. Before treatment the oven dried density was calculated. The weight loss after treatment resulted from the lowest to the highest temperature respectively 3.57, 5.33 and 9.46%. It was noted a small decrease of hardness for temperatures up to 200°C, while for higher temperature the hardness decreased considerably, up to 20%. Decrease of hardness in tangential section was lower than in radial one. From the perspective of utilisation it seems that Albanian beech wood treated at temperatures up to 200°C presents a suitable choice for indoor and outdoor stairs, floor tiles and parquet.

Determination of Accuracy and Reliability of Portable Hardness Testers

The paper is focused on determination of the accuracy and reliability of static and dynamic (portable) hardness testers. The paper deals with the measurement of hardness of calibration hardness plates by 4 different methods (Brinell, Vickers, Rockwell and Leeb) with using 5 different hardness testers (3 static and 2 portable). The hardness values measured by the different hardness testers were compared to the reference hardness listed in the calibration hardness plates and consequently, the accuracy of these measurements was evaluated. The aim of the work has been to determine the accuracy and reliability of portable hardness testers in comparison with static hardness testers.

Research of impact resistance of nanomodified fiberreinforced concrete

Effects of multilevel modification of concrete structure with complex nanomodifier at nano- and microlevel and polypropylene fiber at macro- and mesolevel on mechanical properties and impact resistance of concrete are presented. Nanomodification with complex nanomodifier, which consists of polycarboxylate ether superplasticizer, ultra- and nanofine mineral additives, provides early structure formation, higher strength at early and later ages. The increasing of the static hardness according to Brinell and Mayer of the nanomodified concrete was indicated the high energy of the bond between the structural elements in the surface layer of nanomodified concrete, as well as the ability of the structure to withstand elastic and plastic deformations under uneven compression load. Incorporating of polypropylene fibre to concrete was increased the impact resistance according to parameter of first crack strength and failure energy and changed the failure pattern from brittle to ductile mode.

Hardness Measurement of Metals—Static Methods

This chapter describes the procedures, characteristics, and applications for static hardness test methods. It addresses test methods that are state of the art, commonly used, or that may find increased use due to certain advantages. The methods addressed are Rockwell hardness testing (ISO 6508 and ASTM E 18), Vickers hardness testing (ISO 6507, ASTM E92, and ASTM E384), Brinell hardness testing (ISO 6506 and ASTM E10), and Knoop hardness testing (ISO 4545 and ASTM E284). The chapter also discusses the advantages and disadvantages of these test methods.

The influence of the share of recycled tire on the rubber mixture properties

Rubber granules of different sizes were obtained by mechanical recycling of waste rubber, which can be used as a substitute for black fillers. The aim of this paper is to estimate the influence of the share of recycled rubber in the static (hardness, wear, repulsive elasticity, permanent deformation by stretching, compression permanent deformation) and dynamic (dynamic modulus of elasticity, damping, hysteresis and Yerzley?s elasticity) properties of mixtures. The study determined the proportion of recycled rubber which does not significantly change the properties of mixtures.