Ways to measure cement content.

Ways to measure cement content.

We are repeatedly requested to find out the quantity of cement in hardened concrete and mortar. The request is generally made for one of two reasons; the most typical being that something has gone wrong and the cause and/or blame for the issue is regarded as associated to cement content. The opposite is that an older structure is being repaired or expanded and it's desired to match the existing materials.There are ASTM standards describing methods to do such determinations, but they are based mostly on quite a lot of assumptions that, in some circumstances, are not valid. This doc seeks to explain what is definitely measured, the supply of potential errors and the way massive they could be, and what may be performed to enhance the probability of reaching a solution near the truth. This is carried out by describing what mortar and concrete are fabricated from, what can be measured, what assumptions are made, and the way the entire puzzle is solved.

Can we actually measure cement content in hardened concrete and mortar? We will measure the raw materials in hardened concrete and mortar, but these data don't essentially give sufficient data to allow us to state the cement content with out some assumptions and qualifications.

WHAT IS IN CEMENT, MORTAR AND CONCRETE?

We start by describing the raw supplies that go into mortar and concrete mixers for sale and by defining some terms. Cement is a generic time period which means "glue." Portland cement is a gray powder that when combined with water types a paste that hardens and gains strength with time. This is the glue that holds mortar and concrete together. When sand or high quality combination is added to paste the mixture is known as mortar which is suitable for skinny cross sections. Grouts, plasters and stuccos are generally special mortars and include a lot the same raw materials. Stone added to mortar makes concrete which can be used in structural or huge applications.

Cement

The cement most frequently utilized in building is named portland cement. There are other varieties of building cements, some utilized in masonry construction and different particular cements used for repairs or excessive temperature applications. This paper addresses portland cement and its derivatives only.The predominant chemical compounds in portland cement are based upon oxides of calcium lime, silicon silica, aluminum alumina and iron. There are other compounds current in smaller portions akin to magnesia and carbon dioxide and plenty of trace elements. The principal chemical compounds that combine with water hydrate to provide power are calcium silicates. Nevertheless, in all reported chemical analyses, the constituents of cement and concrete are reported simply as the appropriate oxides. The way in which wherein these compounds mix is extraordinarily complex and out of doors the scope of this paper. Modern portland cements, by definition, all are inclined to include these compounds in a fairly tight vary of values even if they come from completely different manufacturing facilities. Hydrated portland cement has the unusual, and fascinating, property that it's going to proceed to achieve energy albeit at a lowering fee when within the presence of water. This complicates chemical analysis as a result of the system is continually altering from the time of first mixing to the time of test.

A source of further complication is when historic supplies are being examined as a result of the composition and fineness of cement made in 1920 is not the same as that made in 2000. Masonry cements are normally a blend of portland cement, crushed limestone and a few polymeric additives. The producers don't publicize the relative amounts of portland cement and limestone however ASTM requirements do set out ranges into which the blends should fall. It's these blends that tend to cause the most complicated analyses and the broadest vary of assumptions within the method.

Aggregates

The aggregates utilized in mortar and concrete are constructed from the same building blocks: lime, silica, alumina and iron oxide. Some aggregates may be physically separated from hydrated portland cement by their differing solubility in acid. Aggregates are likely to fall into two very broad classes, these containing primarily silica and people containing mainly calcium and magnesia. Siliceous aggregates are usually insoluble in acid, however not always, and this is the supply of one essential assumption made by ASTM C 1084. Calcareous aggregates are soluble in acid, but usually don't contain soluble silica – one other assumption.Supplementary Cementing Supplies

Different supplies coming into the market are the so-called supplementary cementing supplies corresponding to fly ash and slag. These are often waste materials that contain related compounds as portland cement, albeit in differing proportions. By virtue of their chemistry, glassy state and fineness they may react beneficially with portland cement. They're both added to concrete to scale back costs, or to boost properties. It's troublesome to differentiate between these materials and cement in a hardened concrete. The range of their chemical compositions is massive, further complicating the interpretation of chemical analysis.Unhydrated particles of fly ash and slag might be observed using microscopical methods, and an experienced analyst can estimate the quantity of residual fly ash and fly ash present. The presence of slag can be qualitatively indicated by testing for the presence of sulfides. The extremely small measurement of silica fume particles one other supplementary cementing material, and the low dosage normally added makes definitive detection of this materials difficult.

Chemical Admixtures

Chemical compounds, typically in liquid form, are sometimes added to cementing supplies so as to modify or enhance the properties of the plastic or hardened concrete. They are generally added in very small doses and their presence doesn't normally interfere with cement content material determination.

WHAT DO WE MEASURE?

It's not ample to only measure the chemical composition of the hardened materials to determine cement content as a result of all the constituents of hardened concrete contain the same chemical elements. This section describes what different means can be utilized to enrich the chemical analysis.

Chemistry

The basic procedure is to take a consultant pattern of the mortar or concrete, crush it to a nice powder, dissolve it in acid and then use commonplace chemical analytical techniques to measure the relative proportions of calcium, silica, alumina, magnesia. The amount of insoluble residue is also determined and assumed to be aggregate. A portion of the sample can be heated to one thousand°C and the loss in mass measured at sure temperatures. These losses symbolize totally different phases of the material including water and carbon dioxide breaking down into gasoline and leaving the sample. The original unit weight of the pattern can be a useful parameter that's usually determined. The reliability of these analyses is strongly influenced by the sampling methods used. The scale and number of pieces of mortar or concrete taken from the structure should be enough to represent the concrete being tested. The ASTM methods specify minimum sample sizes, but it is not unusual to obtain much smaller samples from the field. These analyses are sometimes the ones that cause problems.Petrography

Petrographic microscopical evaluation of the sample is invaluable in addressing a lot of questions:

What kind of cement has been used?

Does the pattern contain fly ash, slag, ground limestone or other mineral admixtures, and if that's the case, roughly how a lot?

What's the mixture kind and is it probably soluble in acid?

What's the water – cement ratio?

What's the extent of hydration?

What's the condition of the sample?

Are there deposits or contaminants?

Has leaching eliminated constituents?

Not all of those questions can always be answered, and infrequently the solutions are given as ranges of values, all of which should be constructed into the ultimate interpretation. Microscopical point-count methods may be helpful in determining the presence and amount of fly ash, however this strategy requires refinement.

ASTM C 1084 – STANDARD TEST METHOD FOR PORTLAND-CEMENT CONTENT OF HARDENED HYDRAULIC CONCRETE

The broad approach in C1084 is to make use of analytical chemical means to measure soluble calcium oxide, silica and insoluble residue. Allowing for the aggregate kind and composition, the amount of soluble oxide is attributed to the cement, and used to calculate the total cement content. Equally the insoluble materials is attributed to the mixture and used to calculate the aggregate content.The method makes the following assumptions and qualifies itself accordingly:

There are not any supplementary cementing materials.

Soluble calcium oxide and silica contents of cement are assumed as fixed values unless given from one other source.

Soluble silica and calcium in combination is assumed to be negligible where appropriate.

If any of these assumptions are not right the results of the evaluation are prone to be inaccurate. Many aggregates comprise soluble calcium and / or soluble silica, while supplementary cementing materials are soluble. The ASTM technique recommends that the type of mixture be assessed but doesn't require a petrographic examination. Because of this even strict compliance with the strategy is no assure of discovering out what went right into a given concrete sample.

ASTM C 1324 – STANDARD TEST METHOD FOR EXAMINATION AND ANALYSIS OF HARDENED MASONRY MORTAR

Exams on mortar are sophisticated by the larger range of cementing binders used, and by the frequent addition of floor limestone or hydrated lime into the mix. The essential chemical evaluation of the sample is just like that performed on concrete. The strategy additionally requires that a petrographic examination be carried out with a purpose to ascertain what elements have been used in the mortar, i.e. masonry cement, masonry lime, and sort of aggregate. Estimates are also made of the air content, water – cement ratio and diploma of hydration. All of those are used as inputs into the matrix when solving the chemical calculations. This methodology is somewhat empirical in that estimated values are in contrast with results from calculations based on assumptions and measured data. The assumptions are modified based on the observations so as to deliver the two sets of data into agreement. This kind of iterative practice is at the heart of engineering calculations, however is unsettling to pure scientists. What it does mean is that any set of reported results are open to some variation, the extent of which is tough to evaluate, and could also be large. Once more, the tactic shouldn't be a black field that takes a restricted set of inputs and returns a neat, absolute, result.

WHAT IS NEEDED?

It will be significant that a sufficient variety of concrete samples are extracted in order that at the very least 1 kg 2.2 lb is offered for chemical evaluation, with sufficient remaining for petrographic analysis. Two 4 x 8 inch cores are a minimum when concrete is being assessed.For mortar, ASTM C 1324 requires a minimal sample of 10 g. Samples extracted from at the least two zones are fascinating – one set from the concrete in query and one other from similar concrete that's considered acceptable. It's then attainable to report on differences between the concretes with some confidence, even if the absolute answers are difficult to extract.

Ideally, the concrete batch materials cement, supplementary cementing materials and aggregates needs to be supplied, in which case the amount of every materials in the mix can be solved as a set of simultaneous equations.

All details about the aggregate source, mill test certificates for the cements, the usage of supplementary cementing materials and the age of the concrete will help the determination. The more knowledge and material which are provided, the narrower would be the range of error reported at the end of the analysis.

Further more information can be found in measurement of cement content.