,

(9

.7)

К Vg

b

m

a

.

c ρm + ρ a

.

c

Where ρ is density of concrete, kg/m3; Vg is volume of voids between grains

c

c.a

of coarse aggregate; ρb

is bulk density of coarse aggregate; ρ is mortar

c.a

m

density, kg/m3.

For concrete with dense sand, its consumption can be found from condition

of absolute volumes:

Fa=ρc-1.15C-Cp.a, (9.8)

Where F , C, C

are correspondingly quantities of dense sand, cement

a

p.a

and coarse porous aggregates, kg/m3; ρ is density of concrete, kg/m3.

c

178

9.3. Concrete on the basis of organic

(wood) aggregates

Wood wastes without preliminary treatment (sawdust, chips) or after grinding

(slips, hogged chips, wood wool) can be used as aggregates in building

materials on the basis of mineral binders. These materials can be subsumed to

lightweight concrete are characterized by low density (300-800 kg/m3) and heat

conductivity (0.093-0.23 W/(m°С)), and also sufficient workability. Biological

resistance and hard combustibility of the materials on their basis of mineral

binders is provided by impregnation wood aggregates by mineralizers and their

subsequent mixing with mineral binders. Concrete with wood aggregates

blemishes are high water absorption and comparatively low water resistance.

Concrete on the basis of organic aggregates as other types of concrete divides by

application on heat insulating, structural-heat insulating and structural.

179

All types of mineral binders from which Portland cement is the basic one can be

used in the composition with wood aggregates.

For reduction of harmful extractive materials quantity, initial product for wood

aggregates production are seasoned in the storages for a certain time (soft wood

– not less than 2 months, hard wood – 6 months).

At positive temperature seasoning reduces to 1 months at conditions of

subsequent grinding of wood into chips. Hogged chips of soft and especially hard

wood are necessary steeped in the water or solutions of mineral. The last ones

neutralizing action of harmful substances in the wood and fasten cement

hardening in the same time.

9.4. No-fines and aerated concrete

Both lightweight porous and ordinary heavy gravel and crushed stone

aggregates are used for obtaining no-fines concrete. Along with other types of

lightweight concrete no-fines concrete can be used as material for monolithic

and precast wall structures and also for drainage systems and filters.

180

Strength of no-fines concrete depends both on quantity and strength of their

cement content. Last one is defined basically by cement strength and watercement ratio.

Optimal content of cement paste (V ) in no-fines concrete can be found from

c.p

the condition:

V

=

(9