Rapid Hardening Cement

[Catjacob]

Is rapid hardening cement allowed to be used in the construction of piers supporting bridges????????

 

[civilperson]

Yes, in approved mix designs "High Early" cements allow earlier stripping of forms and removal of false work.

 

[LittleWheels]

Early thermal effects can be significantly increased with high early strength mixes, with durability implications.

 

[civilperson]

When the the smallest dimension is greater than four feet, thermal effects can be deleterious. A thermal temperature probe to find internal temperature can be used and insulation of the exterior added to keep the surface and interior at nearly the same temperature. Also pozzolans can be substituted with longer times of hydration and thus lower initial heat gain. Concrete that starts at 70 degrees initial set and gains no more than 10 degrees/hour to a maximum of 145 degrees will have superior early strength and no bad effects with the exterior wrapped to maintain the same temperature as the interior.

 

[cvg]

From Portland Cement Association: "Common recommendations for mass concrete applications include limiting the maximum internal temperature to 70°C (160°F), and the thermal gradient from the interior to the exterior of the concrete section to 20°C (36°F) (higher limits are possible with low coefficient of thermal expansion aggregates)".

http://www.cement.org/tech/faq_mass_concrete.asp#info

 

[Catjacob]

Thank for your advice.

I am thinking whether I can use high strength concrete instead of rapid a concrete made of rapid hardening cement because rapid hardening cement may "posses" some durability problem in long term. If I use say a 60 MPa cube strength OPC concrete, which can achieve compressive strength of at least 30 MPa at 7 days, and strip off the formwork after 8 days the concrete has been placed. What precautious measures or special curing method should be taken if the bridge pier is going to be subjected to a full railway live load from the bridge superstructure after 8 days the concrete has been cast??

 

[LCruiser]

You are going to fully load a railway bridge 8 days after the pier concrete has been poured? That would be interesting. We precast some abutments and replaced a bridge over a freeway with 31 days from traffic diverted to traffic allowed back on. What else is happening before the 8 days? How many days total is it going to be out? No room for a shoefly?

 

[Qshake]

Eight days or not, I would not load concrete until it has proven to meet the minimum specified f'c at that time.

How you get to that point should be decided with the benefit of a materials engineer experienced in mix designs and admixtures and the structural engineer.

Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

 

[Catjacob]

The full storey/question is that the 2-span masonry arch, which carries 2 railway tracks over two carriageways, is going to be demolished and the new replacement bridge is to have a minimum vertical clearance of 5.3m. However, the springline (or the bottom of the arch ring) of the arch is just 3.4 m above the carriageway which implies that the new bridge is at about 1.9m above the springlines of the arches and there should be some vertical elements connecting the new bridge and the tops of the abutments and pier. Unfortunately, there are two restrictions: (A) The existing abutments and piers have to be kept in position and reused (B) The total railway closure time is just 9 days long and the total carriageway closure is just the first two days of the railway closure. Afterwards, either one carriageway can be closed during the railway closure for some preparatory work.
Whatever method of construction is chosen, the tracks and carriageways should be reopened to traffic after the 9-day closure.
My stupid idea is demolish the arch, fix the bars for the “new 1.9m tall dwarf walls” over the pier and abutments and place concrete as quick as possible on the first two days………..
Any better ideas???????

 

[Catjacob]

Another solution I can figure is that use steelwork as the “main skeleton” and concrete is to cover up the steel members. Hence, the vertical steel members will look like a encased column. There are some shear studs on the surfaces of the column so that at some stage in the future, the whole system will evolve into a composite section.
To connect the base of the steel column, I will drill some holes in which bars are inserted and chemical grout (e.g HILTI) is injected into the gaps between the bars and the holes. At last, the base plate is fastened to the pier and abutments................

Does it sound less stupid

 

[civilperson]

High strength concrete and High Early cement can be in the same mix design. They are not exclusive of each other. Steam heating allows precast factories to produce 5000 psi in 8-9 hours and the 28 day strength can be up to 8000 psi. Thus forms can be turned once a day and the cast product is unharmed at release, (worse load condition in the life of the product). A similar heating process can be used in column/arch forms with careful controls as to temperature gain per time.