Theo tiu chun Vit Nam, i vi cng tc b tng:- Tt c mc 100 tr ln u
phi th nghim cp phi: dng ct, xi mng, , nc s dng trn cng trng em v
phng th nghim. Sau khi th nghim s cho 1 kt qu vi mc b tng yu cu th
thnh phn Ct--Xi mng s l bao nhiu.- T ngi ta thi cng da vo iu chnh
cp phi b tng cho ph hp thc t nhm t mc yu cu.* Vi cp phi b tng bn
nu, chc l cp phi theo nh mc 1776 ch khng phi nh mc cp phi th nghim
tng ng vi cng trnh c th, vt liu c th ti cng trng.
- Tr li Vi v d bn hi: + b tng mc 200 1x2 vi cp phi: XM: 281kg,
ct: 0.489, 1x2: 0,8+ Dng my trn 250l trn+ Dng thng sn 20l lng ct (3
thng), (4 thng) vo my trn cho mi m trn. + 1/2 bao xi mng (~ 25kg)Vy
sao tnh c t l theo thng trn?Tr li:Lm theo bc sau-B1: Ngi ta o dung
tch cha ca thng sn (bao nhiu m3): v d 20 lt ~ 20/1000m3 = 0,02 m3.
(1000l = 1m3)- B2: My trn 250l l dung tch ti a. Nhng d trn, ngi ta
cho vo mi m < 3/4 thng trn.- B3: Trn c s cp phi XM: 281kg (5,62
bao XM), ct: 0.489m3, 1x2: 0,8m3 ==> ngi ta tnh ra 0.5 bao XM s
cn:+ 0,5*0.489/5.62 = 0.0435 m3 ct ~ 2 thng sn 20 lt+ 0.5*0.8/5.62
= 0.0711 m3 1x2 ~ 3,56 thng sn 20 ltKt lun:- Cp phi bn cho 1 ng,
nhng khi dng thng sn lng li 1 no. D dng thy rng: lng gn gp i lng
ct, th m bn bn li lng 3 ct - 4 l khng ph hp.Mc b tngl ni n kh nng
chu nn ca mu b tng. Ni d hiu l t l pha trn ct, , nc ckh nng chu nn
ca mu b tng. Mc cng ln (dn th h gi l trn gi hn) th xi mng cng ln
--> cng nn cao.
Nu ly thng b (thng sn nc 18l) lm n v o lng th ta c
T l pha trn cho b tng:
-B tng Mac200 kG/cm (hay 20MPa):01 bao XM - 04 thng CT - 06
thng
-B tng Mac250kG/cm (hay 25MPa):01 bao XM - 03 thng CT - 05
thng
-B tng Mac300kG/cm (hay 30MPa):01 bao XM - 02 thng CT - 04
thng
T l pha trn cho va:- Va mc75 kG/cm: 01 bao XM - 10 thng CT.
- Va mc100 kG/cm: 01 bao XM - 08 thng CT.
D nhin l phi c nc. Ty iu kin nc va .Nu bn s dng nc my t h thng
cp nc th khng cn phi lo. Trng hp bn dng nc ging hay ngun khc th nc
cn phi sch, khng c cht bn. Tuyt i khng dng nc bin, nc phn, nc ao h,
nc l, nc c vng du, m xy nh.
Lng nc ph hp vi t l xi mng s gip cng trnh vng chc.
p dng:Nu bn dng mc thp qu th cng trnh khng t cht lng, nu dng mc
cao qu th lng ph vy trng hp no dng mc bao nhiu (cn na...)
