Post-tensioned expanding concrete with fibers for slabs

Abstract

The present invention concerns a concrete slab, the slab comprising concrete and a combined reinforcement of both post-tension steel strands and fibers, said post-tension steel strands—having a diameter ranging from 5 mm to 20 mm,—having a tensile strength higher than 1700 MPa, said fibers being either steel fibers and being present in a dosage ranging from 10 kg/m3 to 75 kg/m3 or being macro-synthetic fibers and being present in a dosage ranging from 1.5 kg/m3 to 9,0 kg/m3, whereby the concrete is expanding concrete.

1 . A concrete slab, the slab comprising concrete and a combined reinforcement of both post-tension steel strands and fibers,
 said post-tension steel strands   having a diameter ranging from 5 mm to 20 mm,   having a tensile strength higher than 1700 MPa,   said fibers being either steel fibers and being present in a dosage ranging from 10 kg/m 3  to 75 kg/m 3  or being macro-synthetic fibers and being present in a dosage ranging from 1.5 kg/m 3  to 9.0 kg/m 3 ,   whereby the concrete is expanding concrete.   
     
     
         2 . The concrete slab according to  claim 1 ,
 wherein a tensile stress of between 5 and 15% of the final stress may be applied via the post-tension steel strands in the first 24 hours after casting the slab and/or wherein said concrete has a characteristic compressive cube strength of 25 N/mm 2  or higher, preferably 28 N/mm 2  or higher, further preferred 30 N/mm 2  or higher and/or wherein the compression stress at first stressing is between 0.5 N/mm 2  and 7 N/mm 2 , further preferred between 1 N/mm 2  and 5 N/mm 2  or between 5 N/mm 2  and 100 N/mm 2 , preferably 10 N/mm 2  and 75 N/mm 2 , further preferred 15 N/mm 2  and 50 N/mm 2  and/or wherein expanding concrete may comprise one or more additives selected from: CaO, MgO, CaSO 4  or any other additive that may lead to the expansion of concrete during the curing of said concrete and/or wherein   expanding concrete may comprise one or more additives selected from: CaO, MgO, CaSO 4  or any other additive that may lead to the expansion of concrete during the curing of said concrete in an amount of between 5 and 35 kg/m 3  of concrete or expanding concrete, preferably for example between 10 and 30 kg/m 3  of concrete or expanding concrete, further preferred between 15 and 25 kg/m 3  of concrete or expanding concrete and/or wherein the slab or the dimensions of the slab expand by between −5% and 5% during the first 168 hours of curing, preferably by between 0% or >0% and 5% during the first 168 hours of curing, further preferred by between −2.5% and 2.5% during the first 168 hours of curing, further preferred by between 0% or >0% and 2.5% during the first 168 hours of curing, further preferred by between −1.5% to 1.5% during the first  168  hours of curing, further preferred by between 0% or >0% and 1.5% during the first 168 hours of curing, further preferred by between −0.5% to 0.5% during the first 168 hours of curing, further preferred by between 0% or >0% and 0.5% during the first 168 hours of curing, further preferred by between −0.1% or 0% or >0% to 0.1% during the first 168 hours of curing, further preferred by between −0.07% to 0.07% during the first 168 hours of curing, further preferred by between 0% or >0% and 0.07% during the first 168 hours of curing, further preferred by between −0.05% to 0.05% during the first 168 hours of curing, further preferred by between 0% or >0% and 0.05% during the first 168 hours of curing, further preferred by between >−0.05% to <0.05% during the first 168 hours of curing, further preferred by between −0.04% to 0.04% during the first 168 hours of curing, further preferred by between >−0.04% or >0% to <0.04% during the first 168 hours of curing. and/or wherein the tensile stress in the strands of the slab is between 50 MPa and 900 MPa during the first 168 hours of curing, preferably between 100 to 650 MPa during the first 168 hours of curing and/or wherein the slab does not contain any further reinforcement elements, such as rebars or steel nets beside steel fibers and post-tensioning steel strands and/or wherein the slab is cast in one or multiple steps.   
     
     
         3 . The concrete slab according to  claim 1 ,
 wherein said fibers are steel fibers and/or wherein the fibers are glued and/or wherein macro-synthetic fibers may be selected from carbon fibers, glass fibers, basalt fibers or other non-steel based fibers, preferably polyolefin fibers, further preferred polypropylene fibers or polyethylene fibers and/or wherein the steel fibers are present in a dosage ranging from 10 kg/m 3  to 45 kg/m 3 , preferably from 10 kg/m 3  to 40 kg/m 3 , alternatively from ≥25 kg/m 3  to 75 kg/m 3 , preferably from >40 kg/m 3  to 60 or 65 kg/m 3 , further preferred from 15 kg/m 3  to 40 kg/m 3 , further preferred from >20 kg/m 3  to <40 kg/m 3  preferably from 15 kg/m 3  to 35 kg/m 3 , preferably from 20 kg/m 3  to 30 kg/m 3  or from 10 kg/m 3  to <30 kg/m 3  or further preferred from 10 kg/m 3  to 27 kg/m 3  and/or wherein the amount of steel fibers used is below or equal to 1.2 times, preferably 1.0 time, further preferred between >0 and 1.1 times, the amount of steel recommended and used for the steel bars or rebars to be replaced and/or the amount of steel fibers is below or equal to 1.2 times, preferably 1 time, further preferred between >0 and 1.1 times, the amount recommend as rebar or steel bar replacement.   
     
     
         4 . The concrete slab according to  claim 1 , wherein said steel fibers comprise a straight middle portion that have a tensile strength above 1400 MPa, preferably above 1500 MPa, preferably above 1600 MPa, preferably above 1700 MPa, further preferred above 1900 MPa, even further preferred above 2000 MPa, even further preferred higher than 2200 MPa, preferably between 1400 MPa and 3500 MPa. 
     
     
         5 . The concrete slab according to  claim 1 ,
 wherein said steel fibers comprise anchorage ends at both ends,   said anchorage ends each comprise three or four bent sections and/or   wherein said steel fibers have an elongation capacity of between 2.5 and 12%, preferably at least 2.5%, preferably at least 3.5%, further preferred at least 4.5%, even more preferred a least 5.5% and/or   wherein the slab comprising steel fiber concrete is strain hardening in bending.   
     
     
         6 . The concrete slab according to  claim 1 , whereby steel fibers are present in the slab in a dosage ranging from ≥25 kg/m 3  to 60 or 65 kg/m 3 , preferably 20 kg/m 3  to 30 kg/m 3  or alternatively >40 kg/m 3  to 60 or 65 kg/m 3  and/or wherein the fibers have a length of 10 mm to 100 mm, further preferred between >10 mm and 70 mm, further preferred >11 mm and <65 mm. 
     
     
         7 . The concrete slab according to  claim 1 ,
 wherein said supports are concrete supports, masonry supports, steel supports or supports combining concrete, masonry and/or steel and/or   wherein the supports are part of a foundation or preferably the supports are not part of a foundation and/or wherein said concrete slab has a uniform average density and/or wherein said concrete slab is cast in one day and/or in one go and/or be fully casted and/or wherein said concrete slab contains only the fibers and the post-tension steel strands as reinforcement elements and/or and/or wherein said concrete slab is free of a vapor barrier and/or wherein the concrete slab has a thickness for example between 4 cm and 75 cm, preferably between 5 cm and 65 cm, further preferred between 10 cm and 55 cm, further preferred between >10 cm and <40 cm and/or has a width higher than the thickness and/or has a width higher than the thickness and a length higher than the thickness.   
     
     
         8 . The concrete slab according to  claim 1 , whereby the supports may comprise columns, walls, piles or beams or any combination thereof or any other elements acting as vertical support, whereby further such supports can especially be point supports, linear supports or area supports and/or wherein tension is applied to the post-tension steel strands only after the concrete has been cast and the post-tension steel strands remain in place also once the concrete is completely cured/hardened and/or wherein the post-tension steel strands have a tensile strength higher 1800 MPa, preferably higher than 1900 MPa, preferably higher than 2000 MPa, further preferred between 1800 MPa and 4000 MPa and/or wherein the post-tension steel strands have a maximum breaking load of higher than 190 kN, preferably higher than 195 kN, preferably higher than 200 kN, preferably higher than 220 kN, further preferred between 195 kN and 350 kN and/or wherein the post-tension steel strands comprise anchor systems and/or ducts or sheathing. 
     
     
         9 . The concrete slab according to  claim 1 ,
 whereby it further comprises plastic slip-sheets between said concrete slab and the supports, especially at the points of contact between the slab and the supports or whereby plastic slip-sheets are not present between the slab and the supports.   
     
     
         10 . The concrete slab according to  claim 1 ,
 wherein the post-tension steel strands are in a banded-banded steel strands configuration or in a banded-distributed steel strands configuration or in a configuration resulting from any combination thereof, and/or   wherein the post tension steel strands can be arranged in any configuration, preferably without any maximum and/or minimum spacing requirements   wherein the post-tension steel strand are used for bonded or unbonded post-tensioning, and/or   wherein the anchors for the post-tension steel strands are designed so as to reduce bursting behind the post-tensioning anchors during or after post-tensioning, and/or   wherein the fibers are substantially homogenously or homogeneously distributed in the slab.   
     
     
         11 . The concrete slab according to  claim 1 , wherein the slab and the supports are either permanently fully connected, so that the slab is not free to move from its supports, permanently fully disconnected, so that the slab is free to move, partially connected, so that the slab is partially free to move in certain directions or temporarily disconnected, so that the slab is free to move at least temporarily 
     
     
         12 . The concrete slab according to  claim 1   said supports being arranged to form a regular rectangular pattern or quadrilateral shape, said concrete slab comprising straight zones connecting the supports via the shortest distance in two directions, i.e. lengthwise and width-wise, post-tension steel strand bundles being present only in said straight zones in a closely-spaced arrangement, where the maximum distance between bundles does not exceed 1.5 m and/or   said supports being arranged to form a regular rectangular pattern or quadrilateral shape, said concrete slab comprising straight zones connecting the supports via the shortest distance in two directions, i.e. lengthwise and width-wise, post-tension steel strand bundles in one direction being present outside said straight zones in a largely-spaced arrangement, where the maximum distance between bundles exceed 1.5 m.   
     
     
         13 . The concrete slab according to  claim 1 , wherein the span of the slabs between two supports for a given thickness is increased by between 5 and 50%, preferably between 10 or 40% or between 15 and 35%, further preferred at least 5%, 15%, 20%, 25% or 30% over a slab with the same slab thickness but without fibers and post-tension steel strands and/or
 wherein the thickness of the slab for a given span between two supports is reduced by between 5 and 50%, preferably between 10 or 40% or between 15 and 35%, further preferred at least 5%, 15%, 20%, 25% or 30%. over a slab with the same span but without fibers and post-tension steel strands and/or wherein the amount of concrete can be reduced for a given slab thickness or a given span over a slab but without fibers and post-tension steel strands by between 5 and 50%, preferably between 10 or 40% or between 15 and 35%, further preferred at least 5%, 15%, 20%, 25% or 30% and/or wherein the combination of post-tensioned steel strands and fibers increases the structural capacity for flexure, deflection, shear, punching shear, structural integrity, temperature resistance and/or shrinkage resistance over a slab without steel fibers and/or steel strands.   
     
     
         14 . A method to obtain a concrete slab according to  claim 1 . 
     
     
         15 . The method according to  claim 14 , comprising:
 casting a concrete slab, the slab comprising concrete and a combined reinforcement of both post-tension steel strands and fibers,   said post-tension steel strands   having a diameter ranging from 5 mm to 20 mm,   having a tensile strength higher than 1700 MPa, said fibers being either steel fibers and being present in a dosage ranging from 10 kg/m 3  to 75 kg/m 3  or being macro-synthetic fibers and being present in a dosage ranging from 1.5 kg/m 3  to 9.0 kg/m 3 ,   whereby the concrete is expanding concrete and   applying a tensile stress of between 5 and 15% of the final stress in the post-tension steel strands in the first 24 hours after casting the slab.