Masonry Magazine January 1970 Page.20
FIGURE 6 PRINCIPAL DETAILS OF ABSORPTIVE MOLD FOR MAKING TEST PRISMS OF GROUT
Grout test prism
Tape
3" x 3" x 1%" wood block
Front block removed for clarity
Cover units with absorptive paper towelling
4-8 x 8 x 16 in. block required
of the grout. Then pour succeeding lifts of grout after waiting 15 to 60 mintues to allow for settlement and absorption of excess water. This also reduces the hydrostatic pressure of the grout thereby reducing the possibility of blowouts. The waiting period depends on weather conditions and absorption rates of the masonry. Reconsolidate each lift by vibrating 12 to 18 in. into the preceding lift. Consolidation of a lift and reconsolida tion of the preceding lift also may be done at the same time. For solid grouted hollow-unit masonry, only alternate cores need to be reconsolidated.
Repeat the waiting, pouring, and reconsolidation steps until the top of the pour is reached. Reconsolidate the top lift after the required waiting period and fill with grout any space left by settle tested. ment shrinkage.
Sampling and Testing of Grout
THE ASTM SPECIFICATIONS for grout (ASTM C476) does not provide for field control. It is a proportion specification. However, some building codes require that compressive strength tests of grout be made in the field. When this test is required, the following procedure is recommended for making the samples:
First, select a flat location where the block mold will remain undisturbed for 48 hours. Place a piece of wood 15% in. thick and 3 in. square on the level surface. Four masonry units with permeable paper, such as absorptive paper towelling, taped to one face shell are placed around the wood block to form the mold. The resulting mold is approximately 3 by 3 by 6 in. high.
Pour the grout into the 3 x 3 x 6 in. mold in two layers. Rod each layer 25 times with a 1 x 2 in. wood puddling stick to eliminate air bubbles. Puddle the bottom layer throughout its depth. Distrib ute the strokes uniformly over the cross- section of the mold. For the upper layer. allow the stick to penetrate about 1½ in. into the underlying layer. After the sec ond lift is puddled, level the top of the prism with a trowel and immediately cover the prism with wet burlap or simi lar material to keep it damp. The prisms are then protected against extreme changes in temperature, and after 48 hours, remove the masonry units and carefully pack them in damp sawdust or sand for transport to the laboratory where they will be stored in a moist room (100 percent relative humidity) until tested.
Cap the specimens in accordance with the applicable provisions of "Method of Capping Cylindrical Con crete Specimens," ASTM C 617. They should be tested in a damp condition in accordance with the applicable provi sions of ASTM C 39 "Method of Test for Compressive Strength of Molded Concrete Cylinders."
The number of grout samples to be taken should be specified before the start of construction. If the number is not specified, take one sample and cast two specimens for each 30 cu. yd. of grout or fraction thereof being placed each day. Also take a sample whenever there is any change in mix proportions, method of mixing, or materials used.
NATIONAL CONCRETE MASONRY ASSOCIATION
P.O. Box 9185. Rosslyn Station. Arlington. Virginia 22209