masonry cemen

huangyhg

masonry cement
we used to prohibit the use of masonry cement in our spec., but i cannot remember why. can someone refresh my memory?
should we still be restricting the use of masonry cement, if we reference astm c-270?

there was an article published by the mason's lime committee around 1990 that reported on tests of mortars made with masonry cement and portland cement with lime.  the tests were carried out at the university of texas at arlington in 1988.  the masonry cement mortar did not perform as well in tensile bond, shear strength and leakage tests.  masonry cement performed particularly poorly in the leakage rates tests.  the difference was attributed to the use of limestone in masonry cement.  apparently, limestone imparts good workability to mortar, but has little cementitious value.
for lower strength mortars, there is not much difference except that masonry cement generally produces a more ductile and 'softer' mortar.  it is a replacement to provide hydraulic materials to replace the impurities that provided these in 'historic' mortars.
portland cement also restores the hydraulic properties to mortars but provides a harder, more brittle, and stronger mortar.
dik
astm c270-08a permites the use of portland cement, mortar cement and masonry cement.
table 1 give the proportion specification requirements for the various types of cements for different mortar types (m, s, n and o). if mortar cement or masonry cements are used, there are several combinations of the different types of cement and lime to acheive the equivalent mortar.
an alternate method of specifying is table 2, which gives the property specification requirements for the various types of cements. in all cases, the compressive strengths and water retention minimums are the same. for air content, the maximum for portland cement and mortar cements are the same, while a slightly higher maximum air content is permitted for masonry cement.
these two specifications cannot be combined and only one method of specifying (proportion or property) can be be used to be enforceable.
as usual, the appendix recommends the use of the lowest strength mortar possible to carry the load, because higher strengths can compromise some properties of the mortar (mainly workability).
i sit on the c12 committee that writes astm c270 and feel they are proper specifications. personally, i like portland and lime, but that is personal and i have no engineering to "hang my hat on". - just old fashioned.
the radical increase in pre-proportioned mortar mixes including sand have made tremendous strides in the uniformity of mortar. if i had a commercial project, i would only permit the use of the large 3000# bags of pre-proportioned mortar. around here, it rare to see conventional site proportioning of mortar even though the outdated specs still permit the old fashioned site proportioning. it is mainly due to the uniformity, predictability from the accurate weighing and the use of dry sand in the bagging. two to four silos can be used (different types of mortar, colored mortar or grout, etc.) on a site in the same space required and can be placed closer to the point of use.
dick
masonry cement is a mixture of portland cement, lime and admixtures.  part of the reason for the poor performance as compared to site mixing of portland cement and lime is that the proportions are proprietary and they are only required to meet the property specifications of the astm standard.  i might add that the committee is loaded with producers.
part of the problem with masonry cement is that if it is mixed in the proportions typical of plain portland cement, it will result in an oversanded mix, which will result in a "softer" mortar but also more porous.  the addition of lime is for workability and water retentivity, but it doesn't help the hardened mortar performance a great deal.
if you try to meet the strength specs of c270 you'll usually come up short with masonry cement.  if you use the proportion spec, you won't know what your strength is and you'll be left with a variably performing mortar that will stick bricks and block together, but will likely have water migration issues, exacerbated efflorescence, and a greater potential for friable mortar in a few years.  
ron-
the article i cited above asserted that the main difference with the permeability of masonry cement mortar was that it used limestone in place of lime.  is that not correct?

the very old series conducted in texas over 20 years ago may have been flawed and did not represent the range of mortar selections offered to professionals today.
i am a traditionalist and personally prefer portland/lime mortar over the the masonry cement/lime and mortar cement/lime mortars, but try to be open to all the facts. because of this, i have generally voted to approve the use of masonry cement and mortar cement mortars based on recognized tests. incidentally, i don't recall mortar cement being included in the texas tests and specifications over 20 years ago since it is a newer product and possibly not available. the advent of international cement company ownership has created a greater interest in the technology of masonry products because it is not now a "ma and pa" industry that produced the masonry cements of over 20 years ago.
astm committees are dedicated to creating consensus standards with a wide distribution of voting members. unfortunately, there is a woefull lack of interest and knowledge by practicing u.s. engineers, so the standards are determined by the public that has the knowledge and interest. even architects have more interest in the properties of mortar.
i had to wait quite a few years to get to be a voting member in order to maintain the balance required. i really do not know what the term "producer" currently means when it comes to arbitratily categorizing the voting members. most of the people on the committee list are are professional engineers that i associated with when sitting on the mjsc committee that created aci 530. there are very few members from cement "producers", because there is a desire to eliminate too much representation from any company and promote individual membership.
when i first joined astm as a professional engineer, i happened to be a professional engineer that worked for a company that "produced" concrete block, but had no interest in the political debate of "portland vs. masonry cement". now, i am an independant consultant and do forensic engineering regarding building performance. there are other fellow engineer members that represent other firms professionally in other factions of the industry that do not always agree. some are fellow memebers of the msjc that created the aci 530. some work for government agencies, national associations, admixture companies, block and brick suppliers, code/standards bodies, contractors and educators that are all professionally interested the proper use of masonry products.
all to often, structural enginners get carried away with high mortar strengths but do not even realize that the testing procedures do not permit meaningful comparison of mortar strengths and masonry unit strengths. i have made 4500 psi (f'm) hollow cmu prisms using 2200 psi mortar - can't remember if it was portland/lime or masonry cement since it was not that important, but the cubes were tested and documented.
i sincerely wish more u.s engineers would be more interested in improving the level of knowledge of masonry. unfortunately, most have never had a class in structural masonry design and are not   
dick-
the reason i outlawed masonry cement from my mortar spec had nothing to do with mortar strength.  it had all to do with fears of water penetration.  there have been a number of famous masonry failures in my area over the last 20 years, and they all involve water penetration.  is it fair to say that masonry cement is still made with limestone instead of lime?
jim
jim -
since you "outlawed" masonry cement, are you from the old west?
i don't know if the current masonry or mortar cements are made from the same sort of limestone fillers (or coarse ground limestone) that were used 20 to 40 years ago. at that time, people casually referred to masonry cement as being made using portland cement, some limestone fillers, mouse droppings and soap. - obviously some of these stories were either folk lore or stories from lime salesmen, myths or excuses from contractors or designers that like to blame a new product.
some old loadbearing specifications from the 1960's required a 50% decrease in the allowable load on a wall if it was not inspected. common sense eliminated that point in the interest of proper specifications and identification of critical area and required special inspections. now, there are 20 story 6" loadbearing concrete masonry structures routinely built without clean-outs because more advanced inspection procedures are being used.
today's masonry cement is different from its old predecessor, because it has to stand up to modern testing and standards. masonry cement may still be made using some lime or limestone in addition to other enhancing additives and admixtures. the critical point is the fineness of the grind of the limestone or fly ash/pozzolanic to make it chemically active instead of just being an inert coarsely ground filler. finely ground limestone will react with carbon dioxide to promote the healing of mortar and concrete just as has been seen in poured concrete.
i rely on the professionals that are interested in masonry being used correctly. these people could easily recommend only one type of mortar because they do not have an interest in cement sales.
if you are concerned with leakage in a masonry wall (which is not a problem with a properly designed cavity wall), the critical point is the head joint where workability and proper workmanship are the critical items and not the cement type. bed joints are not a problem because they are easily compacted because of the induced load from above when they are ready to be tooled. i would be more worried about the particle shape of the sand than whether limestone was used in the manufacture of the cement.
from a structural standpoint, there is no real difference between the different types of mortar mixes since mortar has a very minor effect on the strength of a loadbearing wall. in this situation, the strength of the masonry units is by far the governing factor and can easily be controlled.
dick

dick,
where are 20 storey 6' loadbearing masonry buildings being built routinely without cleanouts?  what type of inspection procedures are being used?  i know in the us you have these "special inspection" requirements, but i don't think that applies in many countries.
i would just like to know so that i can avoid staying in any of those buildings.
hokie66 -
the 15 to 20 story load 6" load bearing concrete masonry buildings were built in brazil starting in the early 1980's. they were build as apartments to be sold.
in the early years, they were built in general, according to the ncma "green book" the was original title was something like "tentative specification for load bearing multi-story structures" before there was an applicable u.s. code. it was patterned after many of the loadbearing multistory building built in southern california in the 1960's. it subsequently became the basis for aci 530 after input from many respected engineers such as jim amrhein and others and adjusted for leass critical seismic regions. the brazilian engineers made many trips to observe the design and construction of the buildings in a seismic zone before going into the design for their less-critcal seismic area.
when talking about the buildings with the design and construction engineers, they said "we use your codes, but we use them better and use modern adaptations and management". the buildings were typically built in groups of 3 to 10 buildings ranging in heights from 12 to 22 stories under a rapid construction schedule because of the rapid growth.
a typical building consisted of a first or ground floor with some areas required larger openings and more open spaces. this level consisted of 12" thick walls (2 - 6" block because thicker units were not made) and some 6" walls. above that (1st floor to internationals and 2nd floor to americans) the walls were 6" partially reinforced concrete masonry. over the large opeinings, a poured in place beam with a variable width extending into the wall above was cast. from the second floor and up, virtually all walls were load bearing with floor spans from 3m to 4 or 5m with a two way cast in place slab from 4" to 6" thick. they were really a "honeycombs" structure. building non-bearing walls was not economically viable.
vertically, the buildings were broken into 3 to 5 sections depending on the elevation with the block strength set for each of the vertical sections. the block were manufactered and identified (color coded to eliminate reading) at the plant after compressive strength based on representative production samples. the block in inventory were always available for additional unit testing.
the reinforcement for each vertical section was determined and shown on the very well detailed drawings. the drawings showed the cores of every block with symbols/cross hatching for grouting and reinforcement. a single drawing could provide all the general construction for the building construction and was posted along with the color coded elevation drawing for block strengths. the excellant engineering and drawings were a key element to the success.
because it was repetitive construction, extra effort was made by the engineers to make the construction "bullet-proof" from a reliability standpoint.
the same mortar and grout was used for all buildings since the minor cost savings could not be justifed by the extra problems of material handling and testing. because there was a thorough testing program prior to construction the relationship between the masonry unit strength and the prism strength was well established the construction and testing of block prisms was minimized or almost eliminated since the block strength were known in advance.
the classic old fashioned "clean-outs" were also minimized by a program of using a video camera to check representative cores to be filled to verify proper construction. the contractor could not permit any walls to be removed, so the standards of workmanship were absolute - if a wall did not pass the man in charge was gone.
the whole process might scare american engineers, but it was manageable and efficient for a series of semi-repetitive buildings using identical details, basic materials with good quality control.
there were some unique methods used due to the method of construction and the ability to make special concrete masonry units for specific applications. reduced height block (2" to 4") were used on the top course of the interior walls and "j" shaped block were used on the top course of the external walls. the lightly grouted/reinforced walls were grouted the full 8' or so height and after the final consolidation, the floor slab was immediately poured and vibrated into the grout in the bond beam. this created a combination bond beam and two-way slab. the constructon schedule was rather quick because of the intended continuity of the structure.
some projects used precast reinforced concrete floor panels/forms that had a thin concrete slab poured on top. some also had precast window elements that were used with shims to create the openings that windows could be set in later. special block were made for 45 degre corners to eliminate the monoteny of a slab sided 20 story building by providing 6' or 8' sections of relief.
it would never work in the u.s. because of the need for good detailed drawings (they are big!!) that can be understood by everyone on the job and the quality controls and monitoring that do not fit the american tradtion. they spent money on engineering drawings, planning and control.
the structures are what would be best described as robust and efficient structurally, confortable to live in with minimal sound or fire threats.
dick