Additional information and conditions from supplementary sources like the Internet,
relevant books and articles, and most importantly the standard testing procedures of
the American Standard for Testing and Materials (ASTM) were used.
This study was developed to help minimize the problem of the construction industry
regarding the waste management, and material scarcity. The researcher considered these
problems as the main reason for the purpose of this study. In order to come up with the
output of this research, which is a design mixture of crushed concrete debris, various tests
and experiments were made that served as the basis of this study and these are the
following: (a) sieve analysis, (b) ball penetration test, (c) slump test and (d) compression
test.
3.4. Evaluation Procedures
The methods used in this research study proved whether the recycled concrete
debris material is acceptable or not, alternative fine aggregate in a mortar mix.
The compressive strength of mortar is sometimes used as a principal criterion for
selecting mortar type, since compressive strength is relatively easy to measure, and it
commonly relates to some other properties, such as tensile strength and absorption of the
mortar. The compressive strength of mortar depends largely upon the cement content and
the water-cement ratio. The accepted laboratory means for measuring compressive
strength is to test 2 in. cubes of mortar. Because the referenced test in this specification is
relatively simple, and because it gives consistent, reproducible results, compressive
strength is considered a basis for assessing the compatibility of mortar ingredients. Field
testing compressive strength of mortar is accomplished with Test Method C 780 using
either 2 in. cubes or small cylindrical specimens of mortar. Perhaps because of the
previously noted confusion regarding mortar and concrete the importance of compressive
strength of mortar is over-emphasized.
Other mortar characteristics that influence general performance, such as aggregate
grading, water retentivity and flow, can be accurately measured by laboratory tests and
are included in ASTM Standards. Water retentivity allows mortar to resist the suction of
dry masonry units and maintain moisture for proper curing. It is the mortar’s ability to
retain its plasticity in contact with absorptive masonry so that the mason can carefully
align and level the units without breaking the bond.
Under laboratory conditions, water retention is measured by flow tests, and is
expressed as the ratio of initial flow-to-flow suction. The flow test is similar to a concrete
slump test, but is performed on a “flow table” that is rapidly vibrated up and down for
several seconds.
Construction mortars require initial flow values on the order of 130 to 150%.
Laboratory mortars are required to have an initial flow of 100 to 115%. Experienced
masons quickly and accurately adjust the amount of mixing water required to produce
good workability, proper flow, and water retention.
Mortar normally begins to harden or set about 2.5 hours after initial mixing. After this
point, retempering will decrease compressive strength by approximately 25%. ASTM
standards require that all mortar be used within 2.5 hours and permit retempering as
frequently as needed within this time period.
Tests have shown that the decrease in compressive strength is minimal if retempering
occurs only 1 to 2 hours after mixing. Mortar that is not used within 2.5 hours or that has
begun to set should be discarded.