Workshop on Cracking and Durability of Reinforced Concrete The Cases Good afternoon. I will present two cases which give a general representation of our, we think, problems concerning the durability of our structures. I took two bridges and calculated the maximum crack widths according to the way I presented earlier. Here we do not question the reliability of the crack width calculation. We assume that the determined crack width is realistic. J.M. Zwarthoed 5 april 2004

Case 1: pre-cast pre-stressed girders with concrete slab J.M. Zwarthoed Case 1: pre-cast pre-stressed girders with concrete slab 5 april 2004 Occurring crack-patterns: Cracks in the top side of the slab : - direct influence of salt; - no regular inspection possible (u.neath asphalt). Cracks in the underside of the slab: - secluded area (less humid, less influence of salt); - difficult to inspect. Case 1 represents a deck of pre-cast pre-stressed girders with a concrete slab on top. In many cases we saw that due to the little amount the transversal reinforcement didn’t meet the ULS-requirements concerning safety and fatigue and therefore need to be strengthened. In this case not. Cracks in the top side are exposed to de-icing salt and there is only inspection possible when the asphalt is removed. Cracks in the underside pose a smaller problem because of the secluded space between the girders.

Case 1: slab properties Bridge deck 19G-101: J.M. Zwarthoed Case 1: slab properties 5 april 2004 Bridge deck 19G-101: concrete slab: K300 (C20/B25) CEM I (Portland); cover top: 30 mm, cover bottom: 20 mm; environmental exposure classification XF4 or XD1/2 rebars QR40 hot rolled steel fs = 329 N/mm2 (FeB 400): - top: 12-190; - bottom: 16-150. These are the properties of the slab. The short time cubical compression strength is about f’ck = 22 MPa. Unfortunately we only know that Portland cement was being used. The exact concrete mixture is not know. The rebars are profiled and the cover is 30 mm on top and 20 mm below.

Case 1: calculated crack width (3) J.M. Zwarthoed Case 1: calculated crack width (3) 5 april 2004 wmax = 0,25-0,30 mm The location and the crack width. Not in this specific case, but in others the crack width might even be 0,5 mm. wmax = 0,25-0,30 mm

Case 2: pre-cast pre-stressed concrete slab J.M. Zwarthoed Case 2: pre-cast pre-stressed concrete slab 5 april 2004 Occurring crack-patterns: in case of statistically undetermined slab, cracks in the top side of the slab: - direct influence of salt; - no regular inspection possible (u.neath asphalt). cracks in the underside of the slab. Case 2 represents a pre-stressed concrete deck. We have got many bridges with this problem. They are ‘fully pre-stressed’ and the rebars function is to limit crack development. The pre-stress strands are applied in metal ducts and the cover on those ducts is at least 50 mm. Will they be affected by corrosion? The crack widths in these cases are much larger wmax = 0,4 mm, Furthermore because the maximum allowed crack width with regard to pre-stressed structures is only wmax = 0,1 mm. Cracks in the top side are exposed to de-icing salt and there is only inspection possible when the asphalt is removed. Cracks in the underside pose a smaller problem because of the secluded space between the girders.

Case 2: slab properties Bridge deck 25G-153: J.M. Zwarthoed Case 2: slab properties 5 april 2004 Bridge deck 25G-153: statically determined concrete bridge deck: C30/37 CEM I (Portland); cover 30 mm top and bottom; rebars: 12-250 FeB 400 pre-stressing: 35·1182 mm2 FeP 1860 These are the properties of the slab. The concrete strength is C30/37. The short time cubical compression strength is about f’ck = 37 MPa. Unfortunately we only know that Portland cement was being used. The exact concrete mixture is not known. The rebars are profiled and the cover is 30 mm.

Case 2: calculated crack width (1) J.M. Zwarthoed Case 2: calculated crack width (1) 5 april 2004 Positive bending (): occurring steel stress This picture shows the crack width in relation to the steel stress in the rebars. The vertical line represents the steel stress in the SLS. The calculated crack width in case of a develop crack pattern is about wmax = 0,33 mm. During the crack development phase crack widths of wmax = 0,4 mm may occur.

Case 2: calculated crack width (2) J.M. Zwarthoed Case 2: calculated crack width (2) 5 april 2004 wmax = 0,3-0,5 mm The location and the crack width. In a few cases locally crack widths of 0,8 mm might occur. How should we deal with that we would like to know too.

Asphalt pavement Concrete deck J.M. Zwarthoed Asphalt pavement 5 april 2004 The usual pavement consists of a layer of dense-graded asphalt of approximately 50 mm and a layer of gap-graded or stone matrix asphalt on top, also 50 mm thick. 50 mm On top of the bridges the pavement consists of two types of asphalt. The bottom layer is a dense-graded asphalt protecting the concrete unless there are cracks or in case of delaminating. On top lies a layer of stone matrix asphalt which allows water to run through. Both layers are approximately 50 mm thick. Concrete deck

Do we actually have a problem? J.M. Zwarthoed Do we actually have a problem? 5 april 2004 Does the type of cement have influence on the progression of corrosion caused by cracks, CEM I, CEM III, or Aluminium-cement? Is there a relation between crack width and corrosion? What would one consider a safe level of crack width with or without the influence of de-icing salt. What do you think about the SLS-check with steel stress dependable maximal permitted rebar diameters and distance? Are we actually dealing with dynamic cracks and what influence does dynamic loading have on the progression of the corrosion process? If the cracks are covered, does this stop the corrosion process? Are there other, even more, important factors we did not anticipate? All we want to know is: ‘Do we actually have a problem?’. There are still different views on the relation between crack width and rebar corrosion, one says: ‘...crack width itself doesn’t matter, any crack will initiate corrosion...’, another says: ‘...crack width does matter, as long as it isn’t a water-bearing crack...’. I wrote down a couple of questions we could keep in our mind during this session and which one we would to discuss later on. Read them. Cement type? Rules for distribution of reinforcement? Relation crack width  corrosion? Dangerous crack width? The effect of dynamic loading? Deceleration of the process? Other aspects?