International specifications for cementious grouts

Not all grouts are the same. In many countries, the term “grout” is understood in different ways. There are two major specifications, the ASTM C1107 and the German DAfStb Guideline, we focus on in our following MC-Pedia article. Read more about their use and differences.

Definitions of “grout” vary. Usually grouts are known as dense fluid mixtures used to fill joints and to underfill columns. Generally, there are cementitious grouts and epoxy-based grouts on the market which already share different raw materials. Epoxy grouts are two-component-products which contain an epoxy resin, aggregates and hardener. Although epoxy grouts share a low water absorption rate, higher compressive strength and chemical resistance, cementitious grouts are more widely used. Epoxy grouts can be up to five times the cost of standard cementitious grouts and are more complicated to apply. The traditional cementitious grout consists of cement, aggregates and additives and is mixed with water only. After mixing, in the fresh state, grouting products have very good flow properties and early high compressive strengths. In this context, grouts differ from conventional concrete because they are particularly flowable, have a high fine content and are capable of swelling – often referred as “non-shrink” performance.

The DAfStb Guideline has been established in Germany and in the widely European market to specify the characteristics of grouts. In the guideline there is a focus on compressive strength, application thickness, flowability, shrinkage and swelling. On the other hand, the standard specification ASTM C-1107 is widely used outside of Europe, especially in the North American market. The test method proofs the consistency, early age height change, height change of hardened grout and compressive strength of cementitious grouts.

In the scope of the German guideline, the maximum grain size is an important characteristic for the determination of the application thickness. It differentiates between “grouting concrete” with a maximum grain size > 4 mm and “grouting mortar” with a maximum grain size ≤ 4 mm. According to this, the maximum thickness is 25 times of the grain size resp. 40 times in the case of early strength class C.

When it comes to the development of the compressive strength, the ASTM specifications set a minimum performance requirement: 7.0 MPa after one day, 17.0 MPa after three days, 24.0 MPa after seven days and 34.0 MPa after 28 days. The DAfStb Guideline on the other hand has only a requirement after 24 h and 28 days. Within this Guideline, there are three different early compressive strength classes, which determine the performance after 24 h (A≥40, 25≤B≤40, 10≤C≤25 N/mm²). All grouts still have to achieve a compressive strength of at least C50/60 after 28 days.

The requirement and measuring equipment for concrete grouts and mortar grouts differ. The DAfStb Guideline inhibits three different flowability classes for concrete grouting and mortar grouting. In the case of grouting mortar, the slump is measured in a standardized flow channel and assigned to classes f1, f2 and f3. With the grouting concrete, on the other hand, a slump cone is placed on a spreading table and filled with grouting concrete. The flow rate is assigned to classes a1, a2 and a3. In the ASTM specification, three different consistency categories are introduced: flowable, fluid and plastic. The measurement of flowable and plastic is fulfilled with a mortar flow table with the applicable provisions of test method C1437.  For fluid grouts, a flow cone procedure of test method C939 is used.

Shrinkage in cementitious grouts is usual under normal circumstances. To achieve a non-shrink grout additives help to achieve no volume reduction after pouring grouts by letting the grout swell. In the ASTM specification, the swelling/non-shrinkage behaviour is measured in the scope of the “Early Age Height Change” with a maximum height change of + 4.0 % and a “Height Change of Hardened Grout” after one, three, 14 and 28 days with a height change between 0.0 and 0.3 %. The DAfStb Guideline has established separate requirements for swelling and shrinkage. Therefore, the swelling performance is measured after 24 h and has to reach at least 0.1 % of volume increase. To determine the shrinkage behaviour the grouts are divided in shrinkage classes where the reduction in volume is measured after 91 days.

All in all the two specifications share some different approaches to define cementitious grouts, but, nevertheless, they ensure the main characteristics: High early compressive strength, flowabilty and a non-shrink performance. MC shares a broad range of cementitious grouts worldwide, either in accordance to the German guideline or the ASTM standard. Visit our product page on our global website to get an overview of our grouting mortars and concretes or go to the websites of our international subsidiaries.