Quality Control Sampling And Testing Masonry

1) Standard Methods Of Testing
2) Sampling And Testing Mortars And Grout
3) Testing Products: See Products Sections
4) Testing Masonry Prisms (Assemblies)
5) Testing Water Permeance (Std. Method ASTM E 514)
6) Guide Specifications For Masonry Testing And Quality Control 7) Post Construction Investigations

During the construction of structural, engineered brick masonry, it may be necessary to provide some method to assure the quality of the work. These controls may be in the form of materials testing to determine that the materials conform to the project requirements. Control tests may also be used to determine the properties of the masonry as it is constructed or for establishing the integrity of masonry on existing structures.

Following are indicated the ASTM standards and test procedures that may be used for quality control of engineered masonry.

Point Loading

Wall failure - hollow masonry wall

1. Standard Methods Of Tests

Brick Masonry Units
Standard Methods of Sampling and Testing Brick and Structural Clay Tile, ASTM Designation C 67.

Mortar and Grout

Standard Specifications for Masonry Cement (Sections 18-27, Methods of Testing Masonry Cement Mortars), ASTM Designation C 91.

Methods of Test for Compressive Strength of Hydraulic Cement Mortars (Using 2-in. Cube Specimens), ASTM Designation
C 109.

Standard Method for Preconstruction and Construction Evaluation of Mortars for Plain and Reinforced Unit Masonry, ASTM Designation C 780.

Masonry Compressive Strength

Standard Methods of Test for Compressive Strength of Masonry Prisms, ANSI/ASTM Designation E447-74.

Masonry Bond Strength

Standard Method of Test for Bond Strength of Mortar to Masonry Units. ASTM Designation E 149.

Standard Methods of Test for Flexural Bond Strength of Masonry, ASTM Designation E 518.

ASTM Standards for CMU: Sampling and Testing Concrete Masonry Units, C 140-75, RD. 1980.

In addition to the above methods of tests, the following methods, while not generally used for quality control, may be used.

Masonry Diagonal Tensile (Shear) Strength

Standard Method of Test for Diagonal Tension (Shear) in Masonry Assemblages, ASTM E 519.

Masonry Flexural Tensile Strength

Standard Methods of Conducting Strength Tests of Panels for Building Construction, ASTM Designation E 72

2. Sampling And Testing Mortars And Grout

2.1. Bond strength of mortars The single most important property of mortar is bond strength, and it is critical that this bond be complete, strong, and durable. The mechanical bond between individual bricks, blocks, or stones unifies the assembly for integral structural performance, provides resistance to tensile stress, and seals against the penetration of moisture. The strength and extent of the bond are affected by many variables of material and workmanship. Complete and intimate contact between the mortar and the unit is essential, and workability influences the ease with which the mortar spreads and covers the surfaces. Rough units have a very porous surface that is highly receptive to the wet mortar and increases adhesion. The moisture content and suction of the units, the water retention of the mortar, and curing conditions such as temperature, relative humidity, and wind combine to influence the completeness and integrity of the mechanical and chemical bond. Voids at the mortar-to-unit interface offer little resistance to water infiltration and facilitate subsequent disintegration and failure if freezing occurs.

All other factors being equal, mortar bond strength increases as compressive strength increases, although the relationship has no direct proportions. Mortar with a laboratory compressive strength of 2500 psi develops tensile bond strength on the order of 50 to 100 psi. Increases in the cement content of the mix increases both these values. However, high cement-low lime mortars are stiff and do not readily penetrate porous unit surfaces, leaving voids and gaps which disrupt the bond. Increasing air content, or adding air-entraining ingredients, lowers both strengths.

Workmanship is also very important in bonding. Full mortar beds must be laid down by the mason to assure complete coverage of all contact surfaces. Once a unit has been placed and leveled, additional movement will break or seriously weaken the bond. The high water retention of cement-lime mortars allows more time for placing units on bed joints before evaporation or the suction of adjacent units alters the plasticity and flow of the mortar. In aligning the masonry, laboratory tests show that tapping the unit to level will increase bond strength 50 to 100% over hand pressure alone.

Diagram

Bond shear test setup

Because of the many variables involved, it is difficult to develop laboratory tests of bond strength that produce consistent results. Flexural bond strength is presently measured by ASTM E518 or C952. (A new test method called the "bond wrench" is currently in the approval process with ASTM.) A simple field test to check adequacy of bond can be made by merely lifting a unit from its fresh mortar bed to determine it the mortar has fully adhered to all bedding surfaces. Good bond is indicated if the mortar sticks to the masonry unit and shows no air pockets or dry areas. Masonry surfaces in contact with mortar should resist a shearing stress of 20 pounds per square inch after curing 14 days.

Bond tensile test

The NW Masonry Guide Table of Contents

Masonry Institute of Washington
Washington State Conference of Mason Contractors