Technical Look: Hermes Technologie and Cementitious Mortars

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March 2016 saw the publication, for the first time in the history of drain and sewer rehabilitation, a German application standard for cementitious mortars (CC and PCC, SPCC). It applies to the whole of the waste water network, from domestic property to receiving system. This technical report covers the background and the experience gained during the first months.

The first flush toilets appeared about 7,000 years ago. The Sumerians had clay wastewater pipes. Both the Greeks and the Romans operated wastewater systems. After the collapse of the Roman empire, this knowledge was forgotten. It was not until the 19th century that the first drainage systems were constructed. Paris entered this field around 1800. About 30 years ago, the network operators started on the rehabilitation of their systems.

Ordinary building materials did not have the durability that we require in our wastewater conduits. At that time, mortars for new build were mixed with an arbitrary sand/cement ratio: there was huge variation in building construction practice. In sewer construction, there were still a great many unanswered questions. When it came to sewer re-lining, forward-looking clients were already asking for test certificates as early as 1982. The German Society for Trenchless Technology (GSTT) set an example early in 2004 with a first directive for the specifications for mortars to be used in the rehabilitation of sewage pipes. The DWA’s technical sheet M-143-17 came out in 2006. This document is currently being revised and will be published in 2017. For the first time, it will cover the requirements for silicate mortars and polymer-based coatings.

In 2016, there is a DIN with which all mortars used in sewer construction must comply. The still widely used specification for Group 3 mortars is now out-dated. European norms such as EN 1504 scarcely take into account the particular requirements of the water and wastewater industries. All mortars used in new build and rehabilitation must meet one of the European norms relating to general mortar standards and, if they are to be used in the wastewater context, also meet DIN 19573.

This is set out in detail in Table 1, together with all the different mortar types.

To distinguish them from ordinary mortars, drain and sewer mortars are designated with the prefix WW, from the English “wastewater.”

Table 1Mortar definitions

WW masonry mortar has a plastic consistency with a grain size of < 4 mm. It is used for laying klinker bricks for conduits and shafts. The job of masonry mortar is to join bricks or natural stone firmly and permanently.

WW jointing mortar has a stiff to plastic consistency with a grain size of < 2 mm. It is used for jointing brickwork, grouting pipe junctions and filling corroded or eroded joints.

WW coating mortars have a plastic consistency with a grain size of between 0.5 mm and 4 mm. They are used for the subsequent coating of concrete, brickwork or steel components in all situations. Coating mortars are applied manually or mechanically. They also serve to restore or improve the static strength of structural components, abrasion resistance and corrosion resistance, and to seal against pressurized groundwater. Coating thickness is normally of the order of 5 to 40 mm. For rehabilitation, coating thicknesses are at least 8 mm.

WW sealing slurries are non-crack-bridging mineral sealing slurries as per DIN 18195-2 for reinforced and non-reinforced concrete and brickwork. Sealing slurries are applied manually or mechanically.

WW bedding mortars have a plastic consistency and a grain size of </=2 mm, and are used for laying tiles, both small and large format ceramic or fused basalt tiles with hooks or a rough surface on the back. They are used in pipes and installations in all situations.

WW injection mortars for the robotic repair or renovation of inlet connections when retroactively sealing leaking structures must meet requirements.

WW injection mortars for filling cracks, stable joints and cavities, and for soil stabilization have a grain size of </= 0.5 mm and a consistency that varies from soft to fluid, depending on the application. Injection mortar is used especially in drinking water protection zones for retroactive waterproofing of leaking structures, for injecting into cracks and for stabilizing the ground.

WW injection mortars with a thinly flowing consistency are also designated liquid mortars. When relining, they are used with a grain size of </= 0.5 mm for filling the annular ring between the liner and the old pipe.

WW injection mortars for relining with non-self-supporting inner sleeves: Highly flowable injection mortar is used when relining with non-self-supporting inner sleeves, to make a tight fit by filling gaps and the annular space between liner and substrate.

WW repair mortars have a plastic consistency and a grain size that is usually </= 4.0 mm. They are used for partial rehabilitation, repair and re-profiling of defective concrete or brick-built structures. It is also used when fitting or patching parts in.

WW shaft-head mortars have a stiff to flowable consistency. Grain size is about </= 4.0 mm. It is used for manhole frame regulation or for other work in the area of the shaft-head.

WW grouting mortars have a flowable consistency and a grain size </= 8 mm. They are used for grouting cavities that are accessible from above, e.g. curved invert tiles. (For manhole frame regulation, see shaft-head mortars.)

WW filler mortars are mortars that fill larger cavities in damaged conduits and restore load-bearing capacity. These mortars must not come in contact with wastewater.

Testing

All tests called for by DIN 19753 are initial tests and need to be demonstrated only once in the life of a product. Tests must be repeated only if there are changes in the raw materials or substantial modifications to the mortar.

The product documentation must indicate the product’s conformity with DIN 19573 as described above. This information does not need to be printed on the bag. Currently, manufacturers issue certificates on request listing those mortars that have passed the tests for characteristics required by DIN 19573. Some mortars have difficulties with the requirements for sulphate resistance. Few mortars pass the tests for class XWW4, whereas the criteria for classes XWW1 to XWW3 are not as rigorous.

Adhesive pull strength

While compiling DIN 19573, we examined whether thickness of coating affects figures for adhesive pull strength. MPA NRW Dortmund carried out comparative tests. Fresh mortar ERGELIT-KBi was applied in thicknesses of 5, 10, 15, 20, 25, 30 and 40 mm to standard concrete slabs that had been blasted smooth. After storage in moist conditions for 27 days, the test samples were pre-drilled on Day 28. The testers established beyond any doubt that the adhesive pull procedure gives correct results only up to a coating thickness of about 15 mm. With thicknesses above 20 mm, results are clearly less satisfactory, and above 40 mm the test samples are so badly damaged that no adhesive pull strength can be measured. The expert team was also aware that adhesive pull strength tests are sensitive to moisture.

Acid resistance

Test methods for assessing the suitability of mortars for drain and sewer construction and rehabilitation were clearly defined for the first time thanks to DIN 19573. A teTwo test methods for the acid resistance of mortars are described in annexes A and B. .

In Annex A, the test method to prove resistance to biogenic sulphuric acid corrosion for the new class XWW4 (formerly XBSK as in DWA-M 211) is described in detail. The causes and effects of this corrosion are illustrated in DWA-M 168. Further details can be found in Sulphide Practical Handbook for the Wastewater Industry [10]. This test procedure goes back to the Hamburg sewerage system guidelines of the 1990s. The subject had been intensively studied in Hamburg since the mid-1980s. Both cases involved an accelerated test technique. As it is impossible to test for proof of resistance to all kinds of acid attack in one trial, two test procedures had to be defined. If the word ‘resistant’ is used here then it refers to a useful life of many decades. It can be assumed that the rates of corrosion that are demonstrated in the laboratory are reached in practice after some 10 years. Both trials are based on comprehensive scientific tests at the Hamburg-Harburg Technical University (TUHH).

The procedure comprises a test in which a mortar’s resistance to BSA corrosion is evaluated in comparison to a benchmark mortar.

Mortar prisms are immersed in sulphuric acid with a pH of 0 for 14 days or a pH of 1 for 70 days. The test parameters pH value and temperature are kept constant. In order to classify the mortar for its corrosion resistance to biogenic sulphuric acid, the prisms that have been immersed in acid are measured for their relative residual compressive strength and depth of corrosion Xf,D.

The specifications for a mortar for an application as listed in DIN 19573 must be such that it can be demonstrated with reasonable certainty that the product has at least the same level of resistance to BSA corrosion as the benchmark mortar. Specifications for sulphuric acid resistance are deemed to be met, if relative residual compressive strengths of 55 percent for pH 0 and 75 percent for pH 1 are achieved.

In order to determine the sulphuric acid resistance of mortars for classes XWW1 to XWW3, another new test method was developed. It is described in Annex B of DIN 19573. For the sake of scientific security, this test was also carried out at other institutions, e.g. at the Weimar MFPA (Institute for Materials Research and Testing). This also involves an ‘accelerated’ test procedure. Acid resistance of mortars is determined by immersion testing prisms in sulphuric acid with a pH of 4 for 4,000 hours (the bath test); and also by grinding up the test samples and dissolving the cement components in sulphuric acid (the powder test). The results are evaluated with reference to a benchmark mortar1.

This technical article was provided by Hermes Technologie GmbH.

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