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 that has cured for less than 28 days is referred to as green concrete . Aggregate type , cement replacements such as fly ash , and admixtures can affect the capacity of some fasteners , and this may not be reflected in the concrete strength as measured in a standard uniaxial compression test . In general , Hilti data reflects testing with common aggregates and cement types in plain , unreinforced concrete . In questionable cases , consult with Hilti Technical Services .
In view of the significantly lower strength of green concrete ( less than 28-day cure ), it is recommended that mechanical anchors not be placed / installed in concretes cured for less than 7 days , unless site testing is performed to verify the fastening capacity . If an anchor is installed in green concrete , but not loaded until the concrete has achieved full cure , the capacity of the anchor can be based on the strength of the concrete at the time of loading . unless otherwise specified , holes should be drilled with hammer drills set in rotation only mode ( i . e . hammering action of the drill turned off ).
CONCRETE BLOCK
Concrete block is the term commonly used to refer to concrete masonry units ( CMU ) made from Portland cement , water and mineral aggregates . CMU blocks are manufactured in a variety
Nominal width of unit in . ( mm )
Minimum face-shell thickness in . ( mm )
Minimum web thickness in . ( mm )
3 ( 76 ) and 4 ( 102 ) 3 / 4 ( 19 ) 3 / 4 ( 19 ) 6 ( 152 ) 1 ( 25 ) 3 / 4 ( 19 ) 8 ( 203 ) and greater 1-1 / 4 ( 32 ) 3 / 4 ( 19 )
Adapted from ASTM C90 - 14 Table 1 .
1 Average of measurements on three units when measured as described in Test Methods C140 .
ACI 318 Section 17.1.2 and CSA A23.3 Section D . 1.2 require adhesive anchors to be installed in concrete having a minimum age of 21 days at the time of anchor installation . For adhesive anchors installed in concrete aged less than 21 days , it is recommended that the design engineer evaluate the anchor design based on the concrete strength at the time of installation and use a bond strength value for water saturated concrete . Site testing is recommended to verify the fastening capacity .
Cutting through concrete reinforcement when drilling holes for anchors should be avoided . If this is not possible , the responsible design engineer should be consulted first .
2.1.3 MASONRY MATERIALS
Masonry is a heterogeneous building material consisting of clay brick , concrete block or clay tile bonded together using joint mortar . The primary application for masonry is the construction of walls which are built by placing masonry components in horizontal rows ( courses ) and / or vertical rows ( wythes ). Masonry components can be manufactured in a wide variety of shapes , sizes , materials and both hollow and solid configurations . These variations require that the selection of an anchoring or fastening system be carefully matched to the application and type of masonry material being used . As a base material , masonry typically has a much lower strength than concrete . The behavior of the masonry components , as well as the geometry of their cavities and webs , has a considerable influence on the ultimate load capacity of the fastening .
When drilling holes for anchors in masonry with hollow cavities , care must be taken to avoid spalling on the inside of the face shell . This could greatly affect the performance of “ toggle ” type mechanical anchors whose length must be matched to the face shell thickness . To reduce the potential for spalling ,
Nominal size ( usually fictitious )
Modular size ( actual )
10 Anchor Fastening Technical Guide Edition 22 | 2.0 ANCHORING FASTENING TECHNOLOGY | 2.1 BASE MATERIALS Hilti , Inc . 1-800-879-8000 | en español 1-800-879-5000 | www . hilti . com | Hilti ( Canada ) Corporation | www . hilti . ca | 1-800-363-4458
16 "
8 "
8 "
7-5 / 8 "
15-5 / 8 "
7-5 / 8 "
of shapes and sizes using light- , medium- , and normal-weight aggregates . Both hollow and solid load bearing CMUs are manufactured in accordance with ASTM C90 .
CMU sizes generally refer to the nominal width of the unit ( 6 ", 8 ", 10 " etc .). Actual dimensions are nominal dimensions reduced by the thickness of the mortar joint .
CMU construction can be reinforced , whereby reinforcing bars are placed vertically in cells filled with grout to create a composite section analogous to reinforced concrete . If all cells , both unreinforced and reinforced , are filled with grout , the construction is referred to as fully grouted . If only the reinforced cells are grouted , the construction is referred to as partially grouted . Horizontal reinforcement may be placed in a wall via a bond beam , which is always grouted . Ladder reinforcement may also be placed in the mortar bed between courses . Grout typically conforms to ASTM C476 and has a minimum compressive strength of 2,000 psi . Concrete masonry units have a compressive strength which may range from 1,250 to over 4,800 psi , although the maximum specified compressive strength of the assembled masonry will generally not exceed 3,000 psi . Both chemical and mechanical anchors may be used in grouted CMU . If voids are present or suspected , mechanical anchors should not be used , and chemical anchors should only