KING MS Cable is a high performance anchoring grout capable of reaching high early and later age compressive strengths. The product can be used in many applications including cable bolting, earth tiebacks for excavation, grouting anchors in tunnel support systems and grouting soil or rock tendons for anchoring piles of other foundation structures. While MS Cable is capable of reaching high early age strengths within 24 hours it is still sensitive to temperature, since the product uses conventional Portland cement-based technology. As with any Portland cement-based grout the lower the temperature of the constituents (i.e. cement and water) and the curing temperature, the longer the grout will take to set, generate heat and begin developing compressive strength. Therefore, a study was undertaken to determine the compressive strength of MS Cable at varying curing temperatures and combinations of curing temperatures.
The test protocol involved batching MS Cable at a plastic temperature of 21°C and then placing the grout cube specimens in a temperature controlled curing apparatus immediately after casting at a curing temperature of either -15°C, 5°C or 21°C. The grout cube specimens were tested for compressive strength at 2 days, 3 days, 7 days, 28 days and 56 days. The curing conditions for each specimen can be seen in Table 1. The average compressive strength for each specimen can be seen in Figure 1 and the relative compressive strength compared to the control (Specimen A) can be seen in Figure 2. It should be noted that the grout cube specimens for Specimen F (cured at -15°C for 28 days and subsequently cured at 5°C until 56 days) were technically frozen prior to setting and any recordable compressive strength can be attributed to the compressive strength of the frozen pore solution as opposed to the mechanical strength provided by the products of hydration of the cementitious ingredients. It should be noted that the grout cube specimens intended for testing at 56 days for Specimen F, were not able to be tested due to deterioration of the samples experienced upon the change in curing conditions.
It can be seen from the data that the grout cube specimens continued to gain strength if they were maintained at a minimum curing temperature of 5°C for 2 days, exposed to a temperature of -15°C and returned to a minimum curing temperature of 5°C (Specimens C, D and E). It can also be seen from Specimen E that the grout cube specimens did not reach sufficient compressive strength after 28 days when exposed to -15°C after only two days of curing at 5°C, but the grout cube specimens continued developing compressive strength once they were exposed to a curing temperature of 5°C from 28 to 56 days. It should be noted that in some cases the compressive strengths of the different specimens in this study are higher than the values reported on the technical data sheet for MS Cable. This is due to the fact that the compressive strength results indicated on the technical data sheet are more conservative in nature, and the specimens in this study were prepared and tested in controlled lab conditions.
After performing this study, it is apparent that in order for MS Cable to meet the compressive strengths indicated on the technical data sheet, the grout must attain a minimum compressive strength of 20 MPa before being exposed to ambient temperatures below 0°C.The early age exposure to a curing temperature of -15°C can be counteracted only if MS Cable is cured for 48 hours at 5°C and subsequently exposed to a minimum curing temperature of 5°C after being exposed to -15°C. This will delay the compressive strength at 28 days but after being exposed to a curing temperature of 5°C, the compressive strength at 56 days is similar to what can be expected from a sample cured in normal lab conditions. In order to ensure that the early and later age compressive strengths meet the requirements of the technical data sheet at a curing temperature of 5°C, the temperature of the dry-blended MS Cable and mixing water should be kept above 21°C.
TABLE 1: CURING CONDITIONS OF MS CABLE CUBE SPECIMENS.
FIGURE 1: MS CABLE COMPRESSIVE STRENGTH IN DIFFERENT CURING CONDITIONS.
FIGURE 2: MS CABLE COMPRESSIVE STRENGTH RELATIVE TO CONTROL (SPECIMEN A) IN DIFFERENT CURING CONDITIONS.
This report is intended for use as a guide only. Please consult the Technical Services Department of King Packaged Materials Company for further information regarding the use of MS Cable for a specific application.