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lateral to vertical pressure ratio for concrete slurry-which
hello guys,
could anybody please tell me which lateral to vertical pressure ratio for concrete slurry do you use to calculate the lateral pressure during pouring the concrete slurry? if you take it as water, it will be 1.0, if you simulate it as earth pressure at rest, it will be 0.5. so which value you guys use in practice? appreciate for your response.
well, it is liquid in the condition of concern, so i would use 1.0.
for formwork, i quote from
manual de la construcción de hormigón
tercera edición inglesa
waddell, dobrowski
mcgraw hill
méxico 1996
"for wall formwork with a rate of pouring less than 7 ft/h
p=150+9000xr/t
over 7 ft/h rate
p=160+43400/t+2800xr/t
r ratio of pouring of concrete ft/h
t temperature of the formwork, farenheit degrees
p is the lateral pressure exerted on the formwork in psf"
from this only 500 issued books' mexican edition
the book precises it is the maximum lateral pressure on the formwork, and it seems it is proposed by aci committee 347 (i have not looked at mcp, but must be there).
hmm, i need be more precise, for it also gives a parentheses after each of the cases above, explaining that
"2000 psf or 150h, the lesser" for both cases. so whilst i look a precise statement in the manual of concrete practice i would assume you apply the formula for the rate, then you apply the formula for the height and pressure is growing from above to a maximum of that given by the formula or 2000 psf, the lesser of the two, a depth under which the lateral pressure would be constant at the maximum value.
it also gives a formula for pouring concrete in columns
p=150+9000xr/t where the parentheses note 3000 psf or 150h
hence it seems it grows with depth till it meets either 3000 psf or the value given at the formula, under which would remain constant.
please note the guidance given through the documents of aci committee 347, formwork for concrete give formulas to indicate form pressures for placement of concrete.
appropriate and monitored pour rates are vital to ensure satisfactory form performance when using the rates. if the rate will be difficult to follow or if the rate is expected to be ignored, designing for full hydrostatic pressure is appropriate, though the cost will be prohibitive.
the concept that an infinitely tall column of concrete will reach a maximum pressure and even out without respect to a pour rate is confusing to me. while aci 347 provides minimum design pressures to be considered, i not aware of any basis to say lateral concrete pressures over 3000psf need not be expected. if the book recommends not trying to come up with a pour rate and placing scenario that would exceed 3000psf for reasons of common materials and constructability, that makes sense, but it is entirely possible to create form pressures above 3000psf and as such, the appropriate pressure must be designed for.
i would suggest purchasing the documents issued by committee 347, 347-04 guide to formwork for concrete or special publication sp-4, formwork for concrete for complete information and appropriate context for the information previously given.
metric pressure equations are available in the documents as well.
hope it helps,
daniel toon
thanks for you guys information.
the pressure on the formwork will be gamma*h, so for concrete, assuming a unit weight of 140 pcf, the pressure will be 140*depth.
i agree with ron. the formulas are for specific pour conditions with concrete that has some slump. i do not belive they are applicable to sluries.
i think everyone may agree on that that if there's no time to show some setting the liquid pressure should be used; i do. by the way, the dynamic effects of vibration inside the concrete must be small for we don't see in the formulation to grow over liquid pressure ... like mere agitation of the liquid.
a slurry is designed to fill its form quickly, therefore little or no "set" is expected. considering that, the "liquid" approach, gamma(h) is used.
slurries do not typically need vibration to consolidate, so vibration loads need not be considered. besides, the more liquid the material is, the less it will support shear transmission, thus negating vibration effects.

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