Laboratory work No.

9
INVESTIGATION OF BUILDING MORTARS

9.1. Calculation of the composition of cement mortar

The purpose of the test. To calculate the composition of cement
mortar according to the data provided.
Procedure. The data meant for calculation of cement mortar
composition are entered in Table 9.4. Then according to the provided
formulae, the composition of composite mortar is calculated.
Table 9.4. Data for the calculation of composite mortar composition
Mark and units of
Parameter Data
measurement
Brand of mortar S in N/mm 2

Compressive strength of fc in N/mm2

cement
Bulk density of cement ρc in kg/m3
Bulk density of sand ρs in kg/m3
Coarseness of sand Ms
Consistence of mortar Sk in cm

The amount of cement (C) required for 1 m3 of sand is calculated

in kilograms according to the formula:
S = kfc (C – 0,05) + 0,4 N/mm2; (9.3)
S − 0,4
C= m + 0,05 in kg, (9.4)
k ⋅ fc
where: S – is grade of mortar in N/mm2;
fc – is compressive strength of cement in N/mm2;
k – is coefficient subject to sand coarseness:
– for coarse sand – 2,2;
– for medium coarse sand – 1,8;
– for fine sand – 1,4.
Then the volumetric portion of sand Sm, as corresponding to the
unit volumetric portion of cement is calculated:

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 ρ
Sm = c , (9.5)
C
where: ρc – is bulk density of cement in kg/m3;
C – is the amount of cement required for 1 m3 of sand in kg.

The volumetric composition of cement mortar is expressed by

the ratio 1 : Sm (one volumetric portion of cement to Sm portions of
sand): 1 : ...
Then the composition of cement mortar is calculated. For testing
the volume of sand VS1 = 0,0025 m3 is used, and the sand amount S1
is calculated in the following way:
S1 = 0,0025 ⋅ ρs in g, (9.6)
where: VS – is the volume of sand in m ; 3

ρc – is bulk density of sand in kg/m3.

The volume of cement used for testing, VC1, is calculated

according to the formula:
0,0025
VC1 = in m3. (9.7)
S1
The amount of cement used for testing, C1, is calculated
according to the formula:
C1 = VC1 ⋅ ρc. (9.8)
The initial amount of water for testing, V1 in l, makes 10 % of
total dry content. The calculated amounts of materials are entered in
Table 9.5.
Table 9.5. Composition of cement mortar
Mark and units of Composition of cement
Parameter
measurement mortar
Amount of sand Sm1 in kg
Amount of cement C1 in kg
Dry content S1 + C1 in kg
Amount of water V1 in l

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 9.2. Calculation of the composition of composite mortar
The propose of the test. To calculate the composition of
composite mortar according to the data provided.
Procedure. The data for the calculation of composition of
composite mortar are entered in Table 9.6 and according to the
provided formulae the composition of composite mortar is
calculated.
The amount of cement (C) required for 1 m3 of sand and the
volumetric portion of sand (S) is calculated according to the formula
provided in Section 5.3.
The volume of lime paste amount K corresponds to the unit
volume of cement:
K = (0,25 ⋅ S) – 0,3. (9.9)
The volumetric composition of composite mortar is expressed as
1 : K : S.
The selected composition: 1: ... : ...
Table 9.6. Initial data for calculation of composition of composite mortar
Mark and units of
Parameter Data
measurement
Mark of mortar S in MPa
Compressive strength of cement fc in MPa
Bulk density of cement ρc in kg/m3
Bulk density of sand ρs in kg/m3
Density of lime paste ρl in kg/m3
Coarseness of sand Ms
Resilience of mortar Sk in cm
After that the composition of cement mortar is calculated. For
the volume of sand used for testing VSl = 0,0025 m3, the amount of
sand S1 is calculated according to the formula:
S1 = VSl ⋅ ρs in kg. (9.10)
The volume of cement (VC1) and the amount of cement (C1) used
for testing is calculated according to the formula:
0,0025
VC1 = in m3, (9.11)
S
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 C1 = VC1 ⋅ ρc in kg. (9.12)
The volume of lime paste used for testing (VK1) and the amount
of lime paste (K1) are calculated according to the formula:
0,0025
VK 1 = ⋅ K in m3, (9.13)
S
K1 = VK1 ⋅ ρk in kg, (9.14)
where: ρs, ρc, ρk – bulk densities of sand, cement and lime paste
in kg/m3;
S and K – amounts of sand and lime paste, expressed in
volume and corresponding to the volume of cement in parts of the
unit;
S1, C1, K1 – amounts of sand, cement, lime paste in kg;
VS1, VC1, VK – volumes of sand, cement and lime paste in m3.

The water amount V1 is taken as 10% of dry content, i.e. of total

amount of S1 + C1 + K1. The calculated amount of materials is
entered in Table 9.7.
Table 9.7. Composition of composite mortar
Mark and units of Composition of
Parameter
measurement cement mortar
Amount of sand S1 in kg
Amount of cement C1 in kg
Amount of lime paste K1 in kg
Dry content S1 + C1+ K1 in kg
Amount of water V1 in l

9.3. Determination of the consistence of fresh mortar (by the

method of rod-sticking)
Before the determination of properties of mortar, the consistence
of fresh mortar is corrected up to the required level measuring by a
rod-sticking method.
Consistence is a measure of flowability and (or) moisture of
fresh mortar and defines deformity of fresh mortar when worked on
by stresses of a certain type. However, consistence is not directly

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related to the behavior of fresh mortar when it is used for building
work.
Usually there is a linear relationship between the value of rod-
sticking determined by this test method and the value of mortar
spreadability determined for the mortar of the same type while
increasing water amount. However, the angle of line inclination will
vary with mortars of different types.
The purpose of the test: by testing a sample of fresh mortar, the
value of rod-sticking is determined according to the depth of vertical
sticking of a certain rod after its free fall from a definite height into
the sample of fresh mortar. The method suits for mortars with
mineral binders and aggregates of normal or of light weight density
when consistence is estimated by a rod-sticking value.
Apparatus: the device with a rod (Fig. 9.1) made of rod stand
with base plate, frame, fastening element with guiding bushes and
fixing screw; cylinder vessel centrally fixed at recessed place for
positioning; sticking rod with scale at the top and fixed plastic rod of
circle section at the base and semispherical end of the same diameter.
The total mass of a sticking rod and plastic rod makes 90 ± 2 g. The
initial position of a sticking rod is fixed at 100 mm above mortar
surface measuring from the bottom of semispherical end of a rod.

Fig. 9.1. The device with a rod

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 A rammer is made of a rigid waterproof rod, approximately
40 mm in diameter and 200 mm long. The ramming surface at the
end of the rammer should be flat and perpendicular to longitudinal
axis of the rammer. The mass of the rammer should be
0,250 ± 0,015 kg.
Procedure. For this test the volume of fresh mortar should be
not less than 1.5 l. Two samples should be tested. The duration of
mixing is measured from the moment of pouring all components into
the mixer.
To avoid false binding before testing, the test mixture should be
slightly stirred manually by a spatula or a smoothing knife for 5–10 s
without any further mixing.
The sticking rod is fixed in its initial position by a fixing screw.
Before measurement the plastic rod is thoroughly cleaned by moist
textile and dried.
The vessel is filled by two layers of mortar and each layer is
compacted by 10 strikes of a rammer to top up the vessel evenly.
The excess of mortar is swept by a knife to make the mortar surface
flush with the top edge of a vessel. Afterwards the surface is no
longer levelled.
The filled vessel is put on the base plate and the fixing screw is
unscrewed to let the rod fall freely from its initial position.
The depth of rod-sticking into mortar is read from the scale,
counting from the lower par of a top guiding bush, correct to a
millimeter.
When the individual values of each tested mortar sample are
received, the average value of rod-sticking is calculated to a
millimeter. If two individual values differ from the average by less
than 10%, this average is considered to be the value of rod-sticking.
If two individual rod-sticking values differ from the average by more
than 10%, the test should be repeated.
The received results of the determination for the consistence of
fresh mortar are entered in Table 9.8.

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Table 9.8. Determination results of fresh mortar consistence (by the method
of rod-sticking)
Mark and units Tests
Parameter
of measurement 1 2
Depth of rod-sticking St in mm
Average value of Stav in mm
rod-sticking
Conclusion. …………………………………………………... .

9.4. Determination of the consistence of fresh mortar

(by the method of spreadability)
The purpose of the test: to determine the value of spreadability
according to the average diameter of a spread fresh mortar sample,
by pouring it into the mould of standard dimensions standing on the
disk of a shake table and shaking it by vertical jerks for specified
times (i.e. lifting the shake table and letting it fall freely from a
specified height).
Apparatus: shake table (Fig. 9.2) consisting of stand, rigid plate
of table, disk, horizontal shaft and eccentric, which lifts it, and
mobile shaft.
A mould of a truncated cone made of steel or bronze,
60 ± 0,5 mm high; inner diameter of mould 100 ± 0,5 mm at the
bottom and 70 ± 0,5 mm at the top. The top surface and edges of the
mould are even. Axes of planes of top and bottom edges of the
mould are perpendicular to the axis of the conical mould.
The minimal thickness of walls of the mould is 2,0 mm.
The rammer consisting of a rigid waterproof rod of
approximately 40 mm in diameter and 200 mm long. The ramming
surface at the end of the rammer should be flat and perpendicular to
longitudinal axis of the rammer. The mass of the rammer should be
0,250 ± 0,015 kg. Caliper, for diameter measuring up to 300 mm
correct to 1 mm; spatula; knife for smoothing.

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