This document reviews the mechanical and microstructural properties of ultra-high performance cementitious composites (UHPCCs). UHPCCs are made of hydraulic cements, fine aggregates, fibers, and have very high strength and durability. The document discusses the composition of UHPCCs and how the addition of nano-silica and fibers affects the workability and mechanical properties. It summarizes several studies that examined how nano-silica impacts strength, pore structure, hydration products, and microstructure through techniques like SEM analysis, XRD, and TGA. The document concludes that 3% nano-silica optimized strength in most cases by refining pores and increasing density, but more than 5% had

1. 1
Prof. Dr. Maan S. Hassan
University of Technology
Prepared by
Mohammed Layth Abbas
Mechanical and Microstructural Properties
of Ultra-high Performance Cementitious
Composites: A Review
Construction Engineering
and Management Branch
June, 2021

2.  What is Ultra-High Performance Cementitious
Composite UHPCC?
Ultra-High Performance Cementitious Composite
(UHPCC) are a new type of composite materials
made primarily from hydraulic cements, fine
aggregates and discrete reinforcing fibers without
standing material properties. UHPCC has been used
extensively throughout the whole world due to its
ultra-high mechanical properties, dense structure,
low capillary porosity and excellent durability.

3.  Composition of UHPCC?
• a large content of cement and silica fume or nano
silica as binder, fine sand of 150–600 µm sizes,
and crushed quartz of about 10 µm sizes. Very
low water-to-binder ratio is also typically used in
UHPCC mixes resulting in reduced workability
that may be managed by adding an effective
superplasticizer (SP).

4.  Annual number of SCI papers on fiber
reinforcement and Nanomodification of
cement composites.
• Figure below compares the annual numbers of Science Citation Index
(SCI) papers on fiber reinforcement and Nano-modification of
cementitious composites, showing that the annual number of SCI
papers has increased at accelerating levels each year from 2015.

5.  UHPCC Workability with Nano-SiO2
 Flowability of Cementitious Composite:
5
Effect of PVA content on slump flow of mixes with and without NS.
[Y. Ling et al.2019]

6. 1-UHPCCs Mechanical Properties:
Compressive and Flexural Strengths:
Compressive and flexural strengths of UHPCCs at different curing ages.
[Rong et al. 2015]

7. 2-SEM Analysis:
PVA fiber reinforced composite without nano-particle. [Zhang et al. 2019]

8. SEM Analysis:
8
PVA fiber reinforced composite containing 2% nano-SiO2. [Zhang et al. 2019]

9. 3-X-Ray Diffraction Quantitative Analysis
(XRD)
X-ray diffraction quantitative analysis result of mortars (CH: calcium
hydroxide; C3S:Alite; C2S:Belite) [Xi et al. 2020].

10. 4- TGA Analysis:
DTA/TG results of N0 and NS3 at the curing times of 7 days. [Rong et al. 2015]

11. 5-Pore Structure Analysis
Effect of nano-SiO2 contents on pore structure of LW-ECC mortars. [Xi et al, 2020]

12. Pore Structure Analysis

13. Filler effect of NS:
13

14. Nucleating effect created by the
nanoparticles:
14

15.  Conclusions:
• Addition of PVA fibers in cementitious composite
decreased slump flow of the fresh composite. The
amount of slump flow decrease increased with
increasing amount (0.3–1.2% by volume) of PVA
fibers. The incorporation of nano-SiO2 particles in
cementitious composites caused further loss of
flowability.
15

16.  Conclusions:
Due to this review, it can be said that compressive
and flexural strength altered with the nano-SiO2
content. The optimum percentage for nano-SiO2 for
compressive and flexural strength was 3% to reach
its maximum. The mechanical properties declined
slightly with further addition of nS (about 5%) due to
agglomeration of nS particles.
16

17.  Conclusions:
 Lower content of Ca(OH)2 specimen with nano particles when
compared to the reference samples. MIP measurements
revealed exhibited that the pore structure of UHPCC can be
refined by adding nano-SiO2. The porosity and the average
pore diameter decreased with the dosage of nano-SiO2 and the
increase of curing times. The microstructure of the sample with
the addition of nano-SiO2 was more dense and homogenous
compared to that without nano-SiO2 particles. It was also
concluded that the inclusion of nano- SiO2 can efficiently
improve the binding between the paste and aggregate.
However, further addition of nano-SiO2 to 5% had negative
effect on the microstructure of cementitious composite due to
the agglomeration of nano-SiO2 particles.
17

18.  Conclusions:
XRD and TGA tests show that the incorporation of
nS leads to consume a large amount of CH and to
produce more C-S-H gels. Besides, MIP analysis
indicates that the filling effect of nS reduces the
porosity of LW-ECC and further refines the pore
structure.
18

19.  Conclusions:
According to the SEM observation, the mortar
containing nS has been shown to provide a more
compact, uniform and dense microstructure in
comparison to nS-free mortar. By observing the ITZ
between FAC and matrix, reducing CH residue and
increasing C-S-H gels play an important role in
improving ITZ. NS also stimulates the pozzolanic
activity of FAC.
19

20. 20