Roy Jones Technical for Concrete Limited June Technical for Concrete Limited

Transcription

1 Roy Jones June 2014

2 OUTLINE Cement is NOT what the television would have you believe i.e. concrete When mixed with water it is the most popular glue in the World

3 OUTLINE Cement is the 2 nd most consumed material per head of Capita in the World its partner is Water, which is the most consumed product per head

4 OUTLINE Cement forms the Glue in a number of CONCRETES Grout which has a maximum aggregate size of 2mm Mortar which has a maximum aggregate size of 4mm Concrete which has a maximum aggregate size greater than 4mm

5 HYDRATION So why don t all products made with cement as the glue resist the penetration of water? When cement is mixed with water it only requires 30% of its own weight of water to fully hydrate This is a Water/Cement (W/C) Ratio of 0.30 Typically Concretes & Mortars have W/C Ratio s of between i.e. more water than is required

6 HYDRATION As an illustration let us look at a good quality concrete Cement content 350 kgs per cu.m. W/C Ratio of 0.50 Compressive strength of 40.0 N/mm 2 We add 175 litres of water to this mix i.e. 350 x 0.50 (Water = Cement content x W/C Ratio) To fully hydrate our 350 kgs of cement we only need 350 x 0.30 = 105 litres of water

7 HYDRATION This leaves us 70 litres of water we added to achieve our compaction but is no longer required by our cement What happens to this 70 litres when the concrete has hardened? The water evaporates and leaves 70 litres of voids as capillaries within the concrete

8 IN SITU These capillaries are very fine so how does water penetrate? If the capillaries are long then the internal friction prevents the water from fully penetrating e.g. In a concrete dam Hoover Dam > 2 million cu.m of concrete

9 IN SITU Water is an incredible material One teaspoon of water contains more molecules than There are teaspoons of water in the Atlantic Ocean It can provide very high forces behind each molecule with a great deal of persistence

10 SOLUTION We try to ensure we are using the least amount of water without compromising placing and compaction Volume of capillaries HALVED

11 SOLUTION We block the remaining capillaries to prevent water passing. Once in place they are extremely durable There are a number of extremely efficient products that perform this task Some require the penetration of a small amount of water to trigger a chemical swelling and so block the capillary Others are physical materials that are deposited during mixing and hardening

12 SOLUTION There are numerous proprietary systems based on cement available today Admixtures for Renders Coatings Slurries Complete pre-packed systems that offer 3 rd Party Accreditation and / or high levels of Quality Control Proven Technology - Cement based renders containing pore blocking admixtures have been in regular use since the early 1900 s

13 SOLUTION BS 8102:2009 Code of Practice for the Protection of below ground structures against water from the ground It covers 3 types of construction: Type A Barrier protection (can be cement based e.g. mortar / render) Type B Structurally Integral protection (usually concrete based) Type C Drained protection

14 SOLUTION Cement based systems are extremely flexible: Both the systems and products based on cement can be used in either Refurb or New Build They are adaptable for use in combinations with all 3 types of waterproofing A, B or C Dual or secondary protection can be installed using a cement based product / system

15 CONCLUSION This has been a very brief overview of the role cement plays in waterproofing building and structures It is by no means comprehensive but gives an insight into the basic of concrete technology and maybe more understanding of how we look at cement based systems Further Information, Training & Advice can be found at