Cite this paper: J D Bapat, Kalpana Karthikeyan, "Cement Based Building Materials", Indian Cement Review, August 2020, pp 48-51 The work on the following cement-based building materials has been covered: dry mix mortar plaster (DMM), cement-based fly ash bricks, AAC blocks and micro-concrete for concrete repair work.

1. www.IndianCementReview.com
48 | INDIAN CEMENT REVIEW | August 2020
Perspective
Cement-based building
materials
C
oncrete is a cement-based building material
used in construction industry on very large
scale. However there are many other cement-
based materials used in to improve the economy,
conserve materials, energy and to reduce the
carbon footprint of construction. This article focuses
on the following four cement-based building materials:
dry mixed mortar (DMM) plasters, cement-based
fly ash bricks, autoclaved aerated concrete (AAC)
blocks, and micro-concrete for concrete repair work
.
DMM plaster
The cement-based DMM plaster is different from
job-site mortar plaster. It is manufactured in a factory
with dedicated facilities for batching and blending of
all the necessary ingredients in the controlled process.
In this way, DMM plaster with well-defined properties
and performance to meet specific requirements and
applications can be produced.
DMM plaster provides excellent technical properties
to meet the stringent performance requirements which
are common in the current construction scenario,
such as crack free surface, no leaching and aesthetic
look. The use of DMM plaster is cost effective, reducing
potential construction problems with the long-term
integrity of structures with a simple materials approach.
The advantages of DMM plaster are wuality controlled
and factory blended to maintain consistently high
quality, excellent adhesion, no cement and sand storage
required at site, reduces wastage, better workability,
suitable for wide range of masonry/concrete
backgrounds, fibre reinforced for shrinkage crack
resistance, aesthetic look due to better finish, and no
leaching.
Most DMM plasters require only the addition of
potable water and mixed with a simple mixer to produce
high-quality fresh mortar for wall application. Normal
curing process is followed. Most of the high-performance
plasters are usually based on extensive development
process and tests in order to achieve the desired materials
properties. The basic raw materials are: cement, filler
and fine aggregate.
The gradation of aggregate and the choice of the
filler are critical. Desirable properties of DMM plaster
in fresh and hardened state are as follows.
 Mixing time: Mixing time of DMM plaster is
one of the important parameters to define its ease
of application for the mason. Dry mortar powder
should quickly mix with water to get the desired
workability.
 Workability retention (pot Life): Workability
retention is the time taken by fresh mortar/concrete
to lose its plasticity. Once the mortar is mixed
with water it has to maintain its workability till
application, for a reasonable period of time:
minimum 60 m in peak summer noon and maximum
90 m in the morning/evening or winter season.
Workability Retention can be measured from the
time of adding water to dry mix till it loses its
plasticity i.e. its nature to stick to wall, when mason
applies. Loss of workability before application
encourages meson to add water to obtain desired
Cement is an intermediate product and is always converted into some
other form to have a useful end product. The authors—JD Bapat and
Kalpana Karthikeyan—take stock of a few new-generation products that
are making inroads in the construction industry.

2. www.IndianCementReview.com August 2020 | INDIAN CEMENT REVIEW | 49
Perspective
workability and such plaster develops cracks after
hardening.
 Drying time: Plaster should get surface-dried after
application, within certain period of time, to start
surface finishing and curing. During the process
of curing, plaster attains its early strength and
binds properly to the substrate (wall/roof top).
Addition of polymers can delay surface drying.
Polymer mixed DMM may also stick to trowel
and the float used for surface finishing, making
the whole process difficult and time-consuming
 Coverage area: Good coverage area of a plaster
offers cost saving to the customer. Coverage area
can be measured by calculating the spread area
for constant thickness. It depends on the bulk
density of plaster. Higher is the density of plaster
lower is the spread area. Density of DMM also
affects porosity. Optimum bulk density should be
obtained balancing the two factors. Typical coverage
can be expressed for 10 mm thickness as: m2/kg
 Rebound loss: Rebound loss of a plaster shows
its capacity to stick to the wall. Lesser is the rebound
loss, lesser the wastage of plaster during application.
Rebound loss depends on many factors, irrespective
of the nature of plaster.
Firstly, it varies from mason to mason. Sometimes
the masons’ handling makes difference in the rebound
loss.
Second factor is the water content of a plaster
mortar. If water is higher than recommended, mortar
applied on the wall slides and does not stick properly.
If water is lesser than recommended, mortar gets
brittle and falls down immediately. Third factor is
“saturation of backing surface”. Any readymade
plaster product should be used only with recommended
water content. Water content fixed by manufacturer
is enough to prepare a workable mix. It is very
important to make backing surface (substrate) wet
till it gets saturated and surface dry. When the surface
is not saturated, it absorbs water from the plaster
and makes it brittle. Similarly, when the surface is
over saturated, excess water makes plaster flowing
down the wall. The surface of application should be
saturated-surface-dry.
 Binding property: The binding of DMM to the
backing surface (wall with red clay bricks, fly
ash bricks or AAC blocks and roof top) must be
tested before application.
 Compressive strength: No standards specifically
mentions about the compressive strength of
cement wall plaster. However, experience shows
it should have strength of at least 7 MPa at three
days.
Cement-based fly ash bricks
The IS 16720: 2018 gives the specification of fly
ash-cement bricks. Pulverized fuel ash or fly ash
(FA) is a byproduct from thermal power stations,
which use pulverised coal as fuel. This national
resource can be gainfully utilised for manufacture
of FA-cement bricks as an alternative to common
burnt clay bricks, leading to conservation of natural
resources and improvement in environment quality.
The FA-cement bricks are made from materials
consisting of FA in major quantity, cement and
aggregate. These bricks are manufactured by mixing
of all ingredients, which are then moulded into bricks
and are de-moulded when sufficiently hardened and
then subjected to curing.
FA and cement together should be considered
as binder. IS specifies, FA content should not be less
than 35%. However, FA could be as high as 65 per
cent depending upon quality of both cement and
FA. It will be worthwhile to find the strength of
FA+ cement mixture, before deciding proportions.
Sand or bottom ash from boiler can be used as
aggregate. Nominal maximum size of aggregate
should be passing 6.3 mm sieve. The typical dimensions
of FA-cement bricks are given in Table 1.
Table 1: Typical dimensions of fa-cement bricks
(IS 16720 – 2018)
Sl.
No
Particulars
Length
(mm)
Width
(mm)
Height
(mm)
1
Standard modular
190 90 90
2 190 90 40
3
Non-modular
230 110 70
4 230 110 30
The mixing of ingredients should be done in
suitable mechanical mixer. The uniformity of mixture
should be tested in terms of color and consistency.
The mixture thus prepared may be compacted in
moulds by hydraulic or vibratory press or hydraulic-
cum-vibratory press and finished to proper size
without broken edges. After demoulding, the bricks
should be protected till they develop sufficient strength,
before curing. Curing can be done with water as per
IS 456, mist or steam, so as to develop sufficient
strength as required by the designated category. Table
2 gives classification of FA-cement bricks on the
basis of 28-day wet compressive strength. The average
drying shrinkage is limited to 0.05 per cent (max).
The water absorption should be below 20 per cent
(mass) for Class up to 10 and below 15 per cent
(mass) for higher classes. Typical FA-Cement bricks
and red clay bricks are shown in Plate 1.

3. www.IndianCementReview.com
50 | INDIAN CEMENT REVIEW | August 2020
Perspective
Table2: Classification of FA-cement bricks (IS 16720 –
2018)
Sl.
No
Class designation
Average 28-day wet
compressive strength
(MPa) Min
1 15 15
2 12.5 12.5
3 10 10
4 7.5 7.5
5 5 5
Advantages of FA-cement bricks over conventional
red clay bricks:
 The strength of common red clay bricks lies in
the range of 3.5 to 5 MPa; whereas that of FA-
Cement bricks goes up to 15 MPa. Strength also
increases over a period of time.
 Lesser water absorption hence requires less water
for curing.
 Uniform dimensions and more dimensional
stability.
 Lesser transit waste.
AAC blocks
They are also known as cellular blocks. Specification
is given in IS 2185 (Part 3). Autoclaved aerated
concrete (AAC) is a versatile lightweight construction
material and usually used as blocks. Compared to
normal dense concrete, AAC has low density and
excellent sound and heat insulation properties. The
density of AAC is in the range of 450-1000 Kg/m3
as against 2300-2500 Kg/m3 for that of the dense
concrete. Plate – 2 shows typical AAC blocks. The
common raw materials used while making AAC are
given in the Table – 3
Table 3: Raw-mix for AAC manufacture
Sl.
No
Raw material Standard
Proportion for AAC
(mass %)
Aggregate:
fly ash
Aggregate:
Sand
1 Cement
IS 269 and
others
6-15 10-20
2 Fly ash/sand
Fly Ash: IS
3812
Sand: IS
383
65-70 55-65
3 Lime
IS 712,
Class C
18-25 20-30
4
Aluminium
powder paste
600 kg/m3 8
5 Water IS 456 w/c ratio: 0.6 – 0.65
The above proportions may vary subject to different
plant practices and requirement of AAC. Quartz-
rich sand and gypsum is also be used in the raw mix.
Aluminium is added as a pore forming agent. Instead,
suitable foaming agent can also be added; however,
that method is out of the scope of the present paper.
The aluminium reacts with soluble alkalies from
cement and calcium hydroxide to form hydrogen
bubbles according to chemical reaction: Al + 2OH-
+ 2H2O → Al(OH)4- + H2
Hydrogen bubbles formed in reaction are
responsible for the pore formation in AAC blocks.
The raw mix is poured in the moulds, after mixing.
The mixture rises in the moulds after formation of
bubbles. It is cured at ambient temperature for about
45 minutes and cut into block pieces of required
unit size, with wires. The blocks are further cured
in the autoclave with high pressure steam, which
also improves their compressive strength. Typical
conditions in the curing chamber are steam pressure
of 4-16 MPa and curing duration of 8-16 hours.
AAC blocks contain more than 80 per cent air
by volume and its mass is about one-fourth of the
red clay bricks, making it the lightest building material.
The comparison of AAC blocks and burnt (red) clay
bricks is given in Table 4.
Micro-concrete for concrete
repair work
Micro concrete is a proportionate mixture of
Portland cement, graded aggregate of 10 mm down
size or 6 mm down size. Micro-concrete also has a
Plate 1: FA-cement bricks vis-à-vis red clay bricks

4. www.IndianCementReview.com August 2020 | INDIAN CEMENT REVIEW | 51
Perspective
non-shrink additive in the mix to limit the plastic
shrinkage up to 0.4 per cent.
It is generally used in sections which are inaccessible
and where there is thick reinforcement. Generally,
micro-concreting is done as a repair job in structures.
The distressed concrete section or spalled concrete
is removed and after application of suitable bonding
agent over the existing surface, micro-concrete is
poured or applied. Micro-concrete is dimensionally
stable and compatible to the existing structural material
and section. It is to be noted that shuttering to be
done leak proof while micro-concreting and proper
curing methods to be followed since the heat of
hydration of micro-concrete is higher than normal
concrete mixes. Micro-concrete is useful for the
following areas of application:
 Repair of damaged reinforced concrete elements,
like slabs, beams, columns, wall, etc., where access
is restricted and compaction is not possible.
 To jacket RCC columns, to increase load-bearing
capacity (Plate – 3)
Table 4: Comparison of AAC blocks vis-a-vis burnt clay
bricks
Sl.
No
Parameter AAC blocks Burnt clay
bricks
1 Mortar
requirement for
joining
Less due to big
size
More due to
small size
2 Precision in
dimensions
More, (+/-) 1.5
mm
Less, (+/-)
5-10 mm
3 Compressive
strength
2-7 MPa 2.5-3 MPa
4 Density Light, 450-
1000 Kg/m3
Heavy, 2300-
2500 Kg/m3
5 Fire resistance More due to air
voids (2-7 h)
Less (about
2 h)
6 Thermal
conductivity
Low, resulting
in energy
saving (0.21-
0.30 W/m.K,
for 450-750
kg/m3 density)
High (0.81
W/m.K)
7 Noise insulation Better for AAC blocks than
clay bricks due to air voids
(45 db for 200 mm thickness)
8 Speed of
construction
High for AAC blocks
compared to bricks, due to
bigger size, lighter weight and
less number of joints.
9 Moisture
resistance
High for AAC blocks
compared to clay bricks due
to discontinuous micro-pores.
Hence longer life for interiors.
10 Fuel consump-
tion during manu-
facturing, for 1 sq
ft area coverage
(kg coal)
0.97 8
The general features and advantages of micro-
concrete are as follows.
 Can be pumped or poured into restricted locations
 Flowable mortar, hence does not require compaction
 Develops high initial and ultimate final strength
 Offers excellent resistance to moisture ingress
 Makes repaired sections durable
 Rapid strength gain to facilitate early reinstatement
Free-flowing micro-concrete has been found to
be more effective in comparison with conventional
OPC concrete. When conventional mix of high
strength concrete is used for repair, small gaps may
remain around the reinforcement steel either due to
poor compaction or settlement, providing a potential
site to initiate corrosion. Free-flowing micro-concrete
eliminates that problem. The mix proportion of
micro-concrete for a typical strength range of 30-50
MPa is given in Table 5.
Table 5: Typical mix proportion for micro-concrete (30-
50 MPa)
Sl No Constituent Mass (Kg/m3)
1 Cement 556
2 Sand* 1112
3 Water (w/c = 0.7) 387
Note: Fine, sharp washed sand from zone III to IV, as per
IS 383 – 2016
May also contain a non-shrink additive to limit plastic
shrinkage < 0.4%
ABOUT THE AUTHORS:
 Dr J D Bapat is with the Development Professional
for Cement and Concrete. Email Email: consult@
drjdbapat.com | Web: www.drjdbapat.com
 Kalpana Karthikeyan is R&D Manager, Sanghavi
Industries
Before After
Plate 3: RCC column jacketing with micro-concrete