Study On The Puncture Resistance Of Pre-Applied Waterproof Membrane

1. Puncture resistance of sheets with different formulation systems

HDPE/EVA system
Use HDPE as the main resin and is modified by adding EVA resin. The effect of EVA resin content on the mechanical properties and puncture resistance of the sheet (thickness 1.0 mm ) was investigated. The results are shown in Table 1 .

Table 1 Effect of EVA resin content on mechanical properties and puncture resistance

As the EVA resin content in the system increases, the tension, tensile strength, and Shore hardness of the sheet continue to decrease, while the elongation at break of the film continues to increase. This is because as the EVA resin content increases, the proportion of vinyl acetate monomer increases, the crystallinity of the system decreases, causing the mechanical properties to decrease, the toughness to increase, and the hardness to decrease. At the same time, the puncture resistance of the sheet tends to decrease with the increase of the EVA resin content, and it can no longer meet the standard requirements when the EVA resin is added to 40%. Considering the mechanical properties and hardness, it is more reasonable for the EVA resin content in the HDPE system to be around 30%.

Puncture resistance of NS06/PP system

Taking NS06 as the main resin, it is improved by adding different proportions and types of PP resins. After experimental verification, the compatibility of different brands of PP resins with NS06 is quite different. Comprehensive evaluation shows that PP T30S and NS06 systems have good compatibility after mixing. The effect of PP T30S resin content on the mechanical properties and puncture resistance of the sheet (thickness 1.0 mm ) is shown in Table 2 .

Table 2 Effect of PP T30S resin content on mechanical properties and puncture resistance

With the increase of PP T30S resin content in the system, the tensile force, tensile strength, puncture resistance and Shore hardness of the sheet all showed an increasing trend. Among them, the tensile force and puncture resistance were greatly affected by the PP T30S resin content. With the increase of PP T30S resin content, these two indicators increased rapidly, while the elongation at break of the film showed a downward trend. When the PP T30S resin content increased to 40% , the sample broke as soon as it was pulled during the test, and could not meet the requirements of mechanical performance indicators.

At the same time, with the increase of PP T30S resin content, the hardness of the sheet increases rapidly, which cannot meet the actual application construction requirements. Comprehensive evaluation shows that the use of PP T30S resin modified NSO6 with a content of about 35% can meet the standard requirements, and the sheet is moderately hard and soft, meeting the construction application requirements.

2. The influence of sheet thickness on puncture resistance

The puncture resistance performance evaluates the ability of waterproof membrane to resist damage from external hard objects. Waterproof membranes of different thicknesses have different adaptability to the environment during actual construction and application.

In order to facilitate comparison with other variables, the design is based on a 1.0 mm thick sheet. Taking the formulation system with HDPE as the main resin and EVA resin content of 30% as an example, the effect of different sheet thicknesses on the puncture resistance performance was investigated, and the results are shown in Table 3 .

Table 3 Effect of different sheet thickness on puncture resistance

In this formulation system, as the thickness of the sheet increases, the puncture resistance increases; when the sheet thickness reaches 0.9 mm or more, the puncture resistance meets the standard requirements, and as the thickness of the sheet increases, the puncture resistance increases linearly. On the premise that other performance indicators meet the standards, when designing a thicker sheet formulation, the hardness of the sheet can be reduced by reducing the proportion of the HDPE main resin in the formulation, which is more conducive to the construction of detailed nodes and improves the overall construction performance.

3. The influence of self-adhesive layer thickness on puncture resistance

GB/T23457-2017 stipulates that the thickness of the self-adhesive layer of Class P membranes shall not be less than 0.25 mm . During the test , it was found that within a certain range, as the thickness of the self-adhesive layer increases, the bonding effect at the overlapping edges of the membranes is improved and the peel strength increases; however, as the thickness of the self-adhesive layer increases, the cost increases significantly; at the same time, during the puncture resistance test, it was found that as the thickness of the self-adhesive layer increases, the puncture head will not pierce the sheet in a short time, thereby increasing the puncture resistance of the membrane.

The reference sheet used in this test is made of 30% EVA resin added to the HDPE system , and the sheet thickness is 1.0 mm . The effect of different self-adhesive layer thickness on the puncture resistance of the sheet is investigated. The results are shown in Table 4 .

Table 4 Effect of thickness of self-adhesive layer on puncture resistance

4. The influence of particle size of anti-sticking protective layer on puncture resistance

The anti-stick protective layer has two main functions. One is to act as an isolation layer, so that workers can walk and work directly on it after the pre-laying of the membrane without the need for a protective layer, thus shortening the construction period. The other is to protect the self-adhesive layer from premature aging due to ultraviolet radiation, and at the same time form full adhesion with the subsequently poured concrete to eliminate water seepage.

There are two mainstream anti-sticking protective layers on the market, one is mullite sand and the other is artificial synthetic sintered sand. The benchmark sheet used in the test is made of 30% EVA resin added to the HDPE system , the sheet thickness is 1.0 mm , and the thickness of the self-adhesive is 0.35 mm . The effects of different types and particle sizes of isolation sand on the puncture resistance of the coil are investigated, and the results are shown in Table 5 .

Table 5 Effect of isolation sand type and particle size on puncture resistance

Isolation sand has an adverse effect on the puncture resistance of the finished coil. The puncture resistance of the sheet after sand coating has a certain degree of decline, so it is necessary to reserve sufficient margin for the puncture resistance when designing the sheet formula. Compared with mullite sand, artificial synthetic sintered sand has certain advantages, with uniform particle size and no sharp edges, and has relatively less adverse effects on puncture resistance.

Original: Zhang Ming China Building Waterproofing Magazine丨Technology  August 27, 2019