2.1 BASE MATERIALS
Direct Fastening Technical Guide , Edition 24
2.0 DIRECT FASTENING TECHNOLOGY
2.1 BASE MATERIALS
2.1.1 BASE MATERIALS FOR FASTENING
The design of modern buildings requires fastenings to be made in a variety of base materials . To meet this challenge , fastener manufacturers have developed many products specifically targeting certain types of base materials . The properties of the base material play a decisive role in the suitability and performance of a fastener . The designer must carefully match the type of fastener with the base material to obtain the desired results .
2.1.2 CONCRETE
Concrete is a mineral building material that is made from three basic ingredients : cement , aggregate and water . Special additives are also used to influence or change certain properties . Concrete has a relatively high compressive strength compared to its tensile strength . Thus , steel reinforcing bars are cast in concrete to carry the tensile forces , and this combination is referred to as reinforced concrete .
Cement is the binding agent that combines with water and aggregate and hardens through the process of hydration to form concrete . Portland cement is the most common cement and is available in several different types , as outlined in ASTM C150 , to meet specific design requirements .
The aggregates used in concrete consist of both fine aggregate ( usually sand ) and coarse aggregate graded by particle size . Different types of aggregates can be used to create concrete with specific characteristics . Normal weight concrete is generally made from crushed stone or gravel . Lightweight concrete is used when it is desirable to reduce the dead load on a structure or to achieve a superior fire rating for a floor structure . Lightweight aggregates are made from expanded clay , shale , slate or blast-furnace slag . Lightweight insulating concrete is used when thermal insulating properties are a prime consideration . Lightweight insulating aggregates are manufactured from perlite , vermiculite , blast-furnace slag , clay or shale . Sand lightweight concrete is made from lightweight aggregate and natural sand . All concrete with a unit weight between 85 and 115 pcf is considered structural lightweight concrete . The ASTM specification and unit weight for each of these concretes is summarized as follows :
ASTM
Concrete Aggregate grading Concrete unit Type Specification Weight pcf Normal Weight ASTM C33 145-155 Sand Lightweight ASTM C330 105-115 All Lightweight ASTM C 330 85-110
Lightweight Insulating Concrete
ASTM C 332 15-90
A nail penetrating concrete needs to create a hole for the shaft by crushing and compacting the concrete . It also needs to withstand hard aggregates while penetrating the concrete matrix without bending excessively or fracturing . When installed properly the fastener achieves a certain embedment depth which is directly linked to the holding values of the fastener .
Values for the ultimate strength of fasteners in concrete are traditionally given in relation to the 28-day uniaxial compressive strength of the concrete ( actual , not specified ). Concrete which has cured for less than 28 days is referred to as green concrete . Aggregate type , cement replacements such as fly ash , and admixtures could have an effect on the capacity of some fasteners , and this may not be reflected in the concrete strength as measured in a uniaxial compression test . Generally , Hilti data reflects testing with common aggregates and cement types in plain , unreinforced concrete . In questionable cases , consult with Hilti Technical Support .
In view of the significantly lower strength of green concrete ( less than 28-day cure ), it is recommended that power-actuated fastenings not be made in cast-in-place concrete which has cured for less than 7 days , unless site testing is performed to verify the fastening capacity . Power-actuated fastening capacity should be based on the concrete strength at the time of installation .
2.1.3 MASONRY MATERIALS
Masonry is a heterogeneous building material consisting of brick , block or clay tile bonded together using joint mortar . The primary application for masonry is the construction of walls which are made by placing masonry components in horizontal rows ( course ) and vertical rows ( wythe ). Masonry components are manufactured in a wide variety of shapes , sizes , materials and both hollow and solid configurations . These variations require that the selection of a fastening system be carefully matched to the application and type of masonry material being used . As a base material , masonry generally has a much
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