Preparation and properties of silica fume@polyure-thane urea cement composites

In this study, a new material was synthesized by compounding silica fume and polyurethane urea, which is used to evaculate the vibration reduction performance of concrete. The mechanical and damping properties of silica fume@ polyurethane urea (SF@PUU) reinforced cement paste were investigated. Also, FT-IR, XRD, TG analysis, and SEM are included. The results indicated that SF@PUU leads to the production of high damping ratio cement pastes. The damping capacities of SF@PUU cement composites, where the damping mechanism included internal, external, and multiphase friction within the cement matrix. Additionally, SF@PUU created a constrained-layer damping structure in cement paste to improve the damping properties. The review confirmed that SF@PUU subjected to proper treatments can be as the replacement to cement in concrete or as a damping filler. However, more investigation is required into the dimensional stability and durability of SF@PUU-based concrete.


Introduction
Concrete is the widely usable man made material in engineering structures, with the ongoing development of cement composites, concrete with high strength, light weight, high toughness, and other properties emerges one after the other, concrete with high damping capacity is one of them [1,2].Damping refers to the characteristic of any vibration system in which the amplitude of vibration gradually decreases due to external actions or inherent reasons of the system itself .The improvement of damping performance of cement-based composites has great development prospect and application value for solving the harm caused by structural vibration.The investigation on the damping properties of cement composites is extensive, emulsion, fiber, rubber, asphalt and other composites to cement, and have been achieved good results [3][4][5][6].
Silica fume (SF), also known as micro-silica, is an amorphous silicon oxide powder, collected as a residue in the production process of silicon and ferrosilicon alloys.Meanwhile, SF is a common cement additive that is the ultrafine non-crystalline by-product of silicon processing [7].Earlier researchers have extensively studied the physical, chemical, and morphological characteristics of SF and have used it in concrete for a variety of applications.Additionally, many researchers have used SF as a substitute for fine aggregate, cement, and precursor for geopolymer, assessed the influence of SF on concrete performance [8,9].When SF is added to concrete, It combines with the calcium hydroxide formed during cement hydration to form more calcium silicate hydrate (C-S-H) gel.This gel fills in the small pores in the concrete, making it denser and more durable.In addition to improving compressive strength, SF also improves bond strength between concrete and reinforcing materials such as steel.This is due to the formation of a strong interfacial transition zone between the two materials, which helps prevent the formation of cracks and improves the overall durability of the structure [10].
Burroughs et al [11].demonstrated that the impact of SF on the rheology properties was statistically significant and proposed the rheology of cement pastes was significantly affected by the physical properties of SF more than any chemical effects.Nochaiya et al [12] reported that the utilization of SF in combination with fly ash was led to a significant improvement on compressive strength of concrete at early ages (pre 28 days) up to 145% using 10 wt%.Furthermore, the addition of SF enhances the ratio of silica (Si) to calcium (Ca) in the mixture, ultimately results in an increase in C-S-H production, which has a positive effect on reducing alkali-silica reactions [13], and calcium oxychloride production [14].The published literature indicated that SF promotes the microstructure become dense, improving strength, durability, ITZ permeability, and paste-to-aggregate bonding [15].Fu et al [16], investigated that the addition of latex or methylcellulose to plain cement paste increases the loss, storage modal and tan σ.Ginerc et al [17] explored the effects of SF additions on the dynamic and static mechanical characteristics of concrete in amounts ranging from 0% to 15% of cement mass.When the quantity of SF addition or replacement rises, the resonance frequencies of concrete specimens tend to fall significantly, and a modest decrease in the damping ratio and dynamic elasticity modulus.
Polyurethane urea is an elastomer substance formed by the reaction of isocyanate components with resin components.Tan et al [18], researched microencapsulation of silica sol through interfacial polymerization of poly(urea-urethane) has resulted in the creation of a novel self-healing material for concrete restoration.Shilin et al [19], crated high performance casting polyurethane elastomers by reacting polyurethane prepolymer (PUP) with diamine chain extenders that had been inhibited by methyl ethyl ketone oxime (MEKO).MEKO considerably improved the polyurethane's tensile strength and toughness.The greatest elongation at break was 1065%, while the highest tensile strength was 35.6 MPa.Therefor, polyurethane urea has great application potential in many aspects.Chen et al [20], prepared polyurethane-based cement composites (PUCC) by utilizing polyurethane with high damping characteristics and adding it to concrete to improve the damping properties of cementitious composites.Experiments show that PUCC has excellent damping properties, and the damping ratio of PUCC reaches 3.168%, which is 123% higher than that of ordinary cementitious composites.Lee et al [21], used high damping polyurethane coated coarse aggregate to prepare a new type of pre-filled concrete and investigate its damping properties.The test results show that the new prefilled concrete has a high damping ratio of 10% and a damping rate of 8.2% in the range of 10 Hz to 200 Hz, which is 10 times and 4.3 times higher than that of ordinary prefilled concrete.
However, dynamic impact loads often occur in engineering, viscoelastic damping materials and concrete composed of constrained damping structure has a very good vibration damping effect, but this vibration damping method of construction requirements are high, so it is not suitable for large-scale application in construction projects, but the combination of viscoelastic damping materials and silica SF to form a filler, which can be used to improve the vibration damping performance of cementitious materials, and the research on the reinforcing effect of SF and PUU on cementitious composites in the dynamic impact loading is relatively small.[22].In this study, heterogeneous stepwise addition polymerization (polymerization reactions carried out in non-homogeneous systems.That is, polymerization processes in which the catalyst, the reaction medium (including monomer or solvent), or the resulting polymer have multiple phases, and are mainly used to describe free radical polymerization reactions.)wasused to create core-shell particles of SF @ PUU.SF was used as the basis, while PUU, a viscoelastic damping material, was used as the damping layer.To create the inner microconstrained damping structure, the core-shell particles were mixed with cement paste as a damping filler.When vibration occurd, the damping performance of cement composites was improved by the shear energy dissipation of PUU, the frictional energy dissipation of the composite interface, and the energy dissipation of the material itself.On the compressive strength and damping capabilities of cement composites, the impacts of various SF and SF @ PUU dosages were examined.Eventually,by integrating microscopic morphology with macroscopic performance change of cement composites, the mechanism of performance change of cement composites was clarified.

Experimental program 2.1. Materials
The cement used in this study is ordinary silicate cement (OPC) with an apparent density of 3.15 g cm −3 , and the cement used complies with the Chinese standard GB175-2020.The specific parameters are shown in table 1.
2.2.Preparation of SF/SF@PUU SF @ PUU was prepared by heterogeneous step-by-step addition polymerization.Firstly, measured 40 ml absolute ethanol and 40 ml deionized water, and mixed evenly.Simultaneously, adjusted the pH value to 9 was used ammonia.Continue to add 10 g silicone powder, mixed well and then added 2 ml 3-aminopropyl triethoxysilane (KH550).After 10 h reaction under stirring conditions, centrifuge, wash and filter the specimen.Finally, dry the product in 60 °C for 6 h, grinded the samples for standby and recorded the product as KH550/SF.1.25 g component B was dispersed in 80 ml cyclohexane, and stirred constantly to fully dissolve for 15 min.Then, added 6.5 g KH550/SF under stirring conditions and gradually raised the temperature to 75 °C.Thereafter, measure 50 ml acetone and 1.38 g component A was mixed and stirred to completely dissolve it to form component A acetone solution.Then the reactant was filtered and washed 3 times with acetone and ultrapure water, and dried the product in a 60 °C for 6 h.Finally, the obtained product was SF@PUU particles after sufficient grinding.The flow chart of SF@PUU particle preparation is shown in figure 1.

Preparation of cement-based composites
Ordinary Portland cement (P.O 42.5) with fineness and density of 335 m2/kg and 3100 kg m −3 , respectively, was used in the tests.The SF and SF@PUU doses were quality fractions of the partly substituted cement in the ranges of 2 wt%, 4 wt%, 6 wt%, and 8 wt%.The water/cement ratio was 0.4 of all groups.For the unnecessary air bubbles created during the mixing process, liquid tributyl phosphate (TBP) was added in an amount of 0.13% (relative to cement grade).To achieve homogeneity, the cement and SF or SF@PUU were first dry mixed in a mixer for 7 min at a speed of 140 rpm, then mixed for an additional 10 min at a speed of 280 rpm.Water was then added to the TBP and stirred for 4 min slowly and 6 min fast.The combination was placed into 20 mm × 20 mm × 20 mm compressive strength molds and 260 mm × 25 mm × 25 mm damping mechanical analysis molds.After 48 h, all specimens were removed and put in a curing room at 20 °C and 95% relative humidity until testing.

Mechanical testing 2.4.1. Compressive test
Standard-sized compression strength specimens require large number of synthetic composites, in order to facilitate the smooth operation of the experiment, so used the size 20 mm × 20 mm × 20 mm for testing 28d compression strength.Three specimens of each group were used to evaluate each mechanical property.

Dynamic mechanical analysis
The damping ratio of reference concrete and modified concrete were investigated using a cantilever beam vibration caused by an impact.In the test, force sensors, acceleration sensor and pulse hardware/software DASP V11 were used.The 25 mm × 25 mm × 260 mm specimen was set on a rigid support, as shown in figure 2. A tiny metal hammer was used manually to provide a modest load shock to the specimen in order to induce free vibration.The acceleration sensor was affixed to the surface center of the specimen with cyanoacrylate adhesive, and the accompanying vibration was converted into an electrical signal.The acceleration sensor was thought to have no effect on the beam's free vibration [23].
During the testing, a computer-based data collection system called DASP, the Coin-v platform for noise and vibration analysis was used to generate time-magnitude (time history) graphs of hammer force and acceleration response signals.For date processing, a scope Modal Analysis program was utilized, which included Fast Fourier Transform (FFT) and Frequency Response Function calculations.The temporal magnitude graphs were converted to frequency-magnitude (m 2 /s) graphs using the scope Modal Analysis tool, and the resonant  frequency (f0) was calculated.The damping ratio was calculated using the half power bandwidth method [24], after finding the reasonant frequency, as shown in figure 2. The damping ratio was calculated as the following formula.
x is damping ratio, dimensionless; f 0 is resonant frequency, Hz; f 1 and f 2 are the frequencies of half-power point, Hz.

FT-IR analysis
The FTIR spectra of SF, SF@PUU, SF@PUU/cement, SF/cement and cement are shown in figure 3.The Si-O-Si stretching vibration(1105 cm −1 ), and Si-O stretching (812cm −1 ) are characteristic absorption peaks of SF.The N-H stretching vibration (3427 cm −1 ), C-H stretching vibration (3427 cm −1 and 2930 cm −1 ) vibrations, C-O-C (1105 cm −1 ) and Si-O stretching(812cm −1 ) are characteristic absorption peaks of SF@PUU.New characteristic peak is observed at 3427 cm −1 , the vibration peak near 3447 cm −1 was caused by the stretching vibration of OH-, which in the water and the chemically bound water in the hydrated calcium silicate gel.There is an extremely strong and narrow absorption peak near 3640 cm −1 group vibration absorption peak of hydroxyl calcium hydroxide [25].The vibration peak near 978 cm −1 is from the bending vibration peak caused by the asymmetric stretching of Si-O in the hydrated calcium silicate [26].The vibration peaks at 668 cm −1 and 467 cm −1 are from the symmetric stretching of Al-O symmetric stretch and the bending vibration of Si-O in the hydrated calcium vanadate [27].The characteristic peak near 1647 cm −1 may be caused by the bending and contraction vibration of -OH in Si-OH.The characteristic peak near 1417cm −1 is caused by the asymmetric stretching of C-O in CO3-.The peak near 875 cm −1 is the C-O bending vibration which is generally caused by the carbonization.Because SF and SF@PUU cement composites are contain SF, and the increase in the intensity of the peak at 1110 cm −1 implied the Si-O group in cement intensifier.
The peak intensity of SF cement composite at 978 cm −1 is higher than cement paste and SF@PUU cement composites, mainly because SF generates more hydrated calcium silicate by pozzolanic reaction in cement.The SF@PUU peak intensity of cement-based composite at 978 cm −1 is lower than SF cement composite.The reason is that PUU hinders the hydration reaction of some cement particles and the pozzolanic reaction of SF, resulting in the decrease of hydrated calcium silicate content in the hydration products of cement composite.

SEM analysis
To further characterize the improvement in the damping mechanism of SF and SF@PUU in cement paste, analyzed the microstructure characteristics of cement paste, SF cement composites, and SF@PUU cement composites are performed.
It can be seen from the figure 4 that the hydration products of cement mainly include gel, three-dimensional network, layered C-S-H gel (figures 4(b), 4(c)) hexagonal block calcium hydroxide (figure 4(b)), and a few needle rod calcium vanadate (figure 4(d)).As observed in figure 5(a), (b), SF appears agglomeration phenomenon, most of the SF particles disappear due to pozzolanic reaction, and there are few of unreacted spherical SF particles.In addition, as shown in figure 5(b), the edge part of calcium hydroxide shows obvious corrosion phenomenon, and small hydrate particles with irregular shape are formed.
Compared with the figure 4, it can be seen that the surface of SF cement composite is more compact.Due to the pozzolanic reaction of SF in cement, which reduces the content of calcium hydroxide and increases the content of hydrated calcium silicate in hydration products Because SF reacts with Ca(OH) 2 and forms secondary C-S-H gels, Behnood and Ziari [28] found that samples containing 6% and 10% SF, respectively, had compressive strengths that increased by 19% and 25%.Siddique [26].reported the improved aggregate-paste bond and improved microstructure as the main causes of SF's effects.Dispersed SF particles fill the gaps between hydration products and unhydrated clinker particles, which is also the main reason for its strength improvement [29].In figure 4(b) it can be seen from the SEM of cement-based composites that spherical SF is embedded in the cement paste after being coated by PUU.By comparing the surface of cement paste, it is obvious that SF@PUU decrease the surface compactness of cement-based composites.The PUU inhibits the hydration reaction of some cement particles, which SF is coated by PUU, which prevents pozzolanic reaction.This also is caused by the strength decrease of SF@PUU cement composites.Further from the figure, it can be seen that the polyurethane and cementitious composites are tightly wrapped, a large amount of SF is bonded to or wrapped by polyurethane, and polyurethane is attached to the cementitious material by virtue of its good bonding strength, and the two are well bonded so as to form an interpenetrating dense mesh structure, which is easy to friction and sliding when subjected to external stresses or impacts, and at the same time, due to the fact that SF and polyurethane At the same time, because SF and polyurethane have strong deformation ability, a large number of polyurethane and SF on the surface of cementitious composite material dissipate energy through their own contraction and expansion and friction with cementitious composite material, which improves the deformation resistance of mortar and increases the damping performance of cementitious material.

Thermogravimetric analysis (TG/DTG)
The Netzsch STA 409 PG equipment was chosen for the thermogravimetric analysis, with an alumina topopened crucible (mass 184 mg and volume 0.085 ml), a sample mass of roughly 30 mg, N2 gas dynamic atmosphere, and a heating rate of 10 °C min −1 to 1000 °C.
Figure 6 illustrates TG-DTG thermograms of specimens for 28 days.The TG/DTG thermograms show three endothermic phase.The first phase located at 50-300 °C is attributed to the C-S-H, C3AH6 and AFt dehydration [30].At this phase, the mass loss of the three specimens are 11.74%, 10.49% and 9.08%.The mass loss of SF cement composite is less than cement paste, mainly because the pozzolanic reaction of SF is weak and  the less content of SF involved in hydration.When the SF replacing cement is large (selected 6 wt% SF cement composite for comparison), the content of hydrated calcium silicate gel generated by the reaction would be reduced.As for SF@PUU cement-based composites, the pozzolanic reaction of SF and the hydration reaction of some cement particles were hindered by the PUU coating of SF, that SF@PUU reduction of hydrated calcium silicate content in cement-based composites.
The second thermal decomposition stage is between 400 °C-500 °C.The mass losses at the second step of TG analyses for three specimens, related to the decomposition of CH, were 3.14%, 2.85% and 3.00% respectively.The mass loss of SF cement composite is less than cement paste, the reason is that the pozzolanic reaction consumed some calcium hydroxide, as a result the content of calcium hydroxide in cement hydration products decreases.And in SF@PUU cement-based composites, SF is coated by PUU, and number of uncoated SF particles involved in pozzolanic reaction, which caused the decrease of calcium hydroxide content.However, PUU will continue thermal decomposition at this step, so its mass loss is higher than SF cement-based composites.
The third decomposition step between 550 °C and 840 °C, which mainly due to the decomposition of CaCO3.The mass loss of the three specimens at this stage are 3.25%, 3.51% and 4.6% respectively.The mass loss of SF@PUU cement-based composites is significantly higher than that of SF cement-based composites, which due to the decomposition of PUU residual in SF@PUU.

X-ray diffraction
A Japan Rigaku D/Max-Ra rotating anode x-ray diffractometer outfitted with a Cu K tube and a Ni filter was used to acquire the XRD patterns, the diffraction angle 2θ = 0-60°.It can be seen from the figure 7 that there is no obvious change in the peak after adding SF and SF@PUU in cement paste.The characteristic peak of calcium hydroxide in cement hydration products are around 2θ = 18.11°, 2θ = 34.08°and2θ = 47.10°.The characteristic peak at 2θ = 32.22°,which may be derived from calcium vanadate in cement hydration products.
The intensity of the diffraction peak is relatively weak at 2θ = 32.09°and2θ = 47.08°, which attributed to CaCO 3 produced by carbonation and C 3 S left by incomplete hydration.From the diffraction peak of SF cement composite, calcium hydroxide (2θ = 18.00°) can be clearly seen, which is mainly due to the pozzolanic reaction of SF in cement.Volcanic ash reaction consumes part of calcium hydroxide and reduces the content of calcium hydroxide in cement, which corresponds to the previous infrared spectrum analysis and TG analysis.Due to Ca(OH) 2 +SiO 2 +H 2 O→C-S-H (gel) and the secondary reaction effect in the later stage , SF enhances the compressive strength of the cementitious materials, which mainly originates from the microaggregate filling effect, and SF@PUU cementitious materials introduced flexible chain segments in polyurethane, so the mechanical strength of cementitious composites decreased, and at the same time, because polyurethane is not involved in cement hydration in the whole process, the intertwining and mismatching of each crystalline phase dissipates energy through friction, which in turn improves the damping performance.

Compressive strength
The compressive strengths of SF-reinforced and SF@PUU-reinforced cement paste at various doses for 28 days of curing are shown in figure 8.The compressive strength of SF cement-based composites are higher than those of ordinary cement at different content gradients.With the content increase of SF, the compressive strength of SF cement composites increases by 17%, 19%, 28%, 33% and 26% respectively.The mainly due to the pozzolanic reaction between SF and cement hydration product calcium hydroxide, which generates more hydrated calcium silicate [31].Secondly, SF particles can fill some pores and defects so that makes the cement surface more dense, and improves the compressive strength of cement composites [32].
The peak value occurred at a dosage of 10 wt% SF, but only a slight increase occurred.This probably due to the pozzolanic reaction of SF is weak at room temperature, and the content of SF involved in hydration is small.When the large amount of SF replacing cement, the content of hydrated calcium silicate gel generated by the reaction would decrease, so the increase of compressive strength is decreased [33].
With the content increase of SF@PUU, the compressive strength of cement composites increased by 3.5% and 0.48%, and then decreased by 17%, 21% and 29% respectively.The reason is that when the dosage is lower than 4 wt%, some cement pores are filled with SF@PUU particles and pozzolanic reaction on a small amount of uncoated SF particles.Also, the introduction of PUU interface reduced the compressive strength, so the increase of compressive strength is not significant.When the dosage exceeds 4 wt%, the interfacial weakness caused by PUU dominates its strength.Therefore, with the increase of content, the strength of cement composites gradually decreases.
Due to the filling effect, SF reduced the porosity of mortar specimens and increased the compressive strength of cement composites.In contrast, the addition of SF@PUU decreased the mechanical strength of cementitious materials, probably due to the poor compatibility of SF@PUU with the matrix of cementitious materials.At the same time, SF@PUU formed a polymer film in cementitious materials, and because the elastic modulus of the polymer was smaller than the elastic modulus of the cementitious materials, the compressive strength of SF@PUU cementitious materials was reduced.SF and PUU both may play a synergistic role in cementitious materials to enhance the mechanical strength of the cementitious materials, but because SF is ultimately small amount of relative to PUU, the macroscopic performance of PUU has more influence on the compressive strength.

Damping properties
According to the test results of compressive strength, five kinds of contents (0 wt%,2 wt%,4 wt%,6 wt%,8 wt%) were selected for damping performance test.

Vibration duration analysis
Figure 9 shows SF and SF@PUU cement-based composites vibration attenuation, the vibration attenuation curves are similar.After 0.07 s, figures 9 (c), (d) shows that the SF@PUU cement-based composites vibration attenuation curve is stable at ± 20 m s −2 , while after 0.2 s the amplitude of cement paste and other groups are stable at about ± 20 m s −2 .Therefore, it is obviously that SF@PUU cement composite with 2 wt% SF@PUU shows the best damping property.

Transfer function analysis
Figure 10 shows SF and SF@PUU cement-based composites change curve of vibration acceleration spectrum that obtained from the transfer function analysis.It can be seen that multiple modal frequencies in the range of 0-2000Hz, including 144 Hz, 197 Hz, 727 Hz and 1120 Hz, which are caused by the resonance at other positions of the fixture under the excitation.Combined with the EMA modal test and finite element simulation, it is determined that the first and second modal frequencies are about 200 Hz and 1200 Hz (shown in figure 11), and the amplitude corresponding to the modal frequency of the specimen should be higher than that of other interference peaks.The transfer function analysis takes modal analysis as the basis to analyze the frequency response function, which determined the first-second order modal frequencies and damping ratio of the specimens.
According to figure 10, in the first mode, the increase of SF content hardly causes few changes to the vibration response peak of cement-based composites.And in the second mode, with the increase of SF content, the peak value response of SF cement-based composites are significantly higher than cement paste, which indicates the introduction of SF reduced the damping performance of cement composites.The addition of SF@PUU reduces the peak vibration response of cement composites, and the peak value of 2 wt% SF@PUU cement composites vibration response decreased by 38% compared with cement paste.

INV damping ration analysis
According to vibration acceleration spectrum and INV damping meter method, the changes of SF and SF@PUU cement composites modal frequency and damping ratio are summarized in table 1.In SF cement-based composites, the first-order modal frequency did not change significantly with the increase of SF content.The second-order modal frequency increased 48 Hz and subsequently decreased 92 Hz which indicated the stiffness of the cement-based composites increased firstly and then decreased, corresponding to the previous changes in the compressive strength of SF cement-based composites [34].In SF@PUU cement-based composites, the first-order modal frequency and the second-order modal frequency are reduced respectively by 6-26 Hz and 288-346 Hz which indicates that the stiffness of SF@PUU cement-based composites decreased correspondingly.
As shown in table 2, in the 175-300 Hz frequency of the first mode, the damping ratio reaches a peak at 4 wt% SF, which is increased up to 18% higher than cement paste.In the 1000-1500 Hz frequency of the second  mode, the damping ratio of SF cement-based composites decreased with the content increase of SF.As for SF@PUU cement composite in the frequency range of the first mode and the second mode, the optimum dosage is 2 wt%, the damping ratio increases by 37% and 6.6% respectively compared with the cement paste.SF coated with PUU can greatly improve the damping performance of cement composites.When the content of SF @ PUU is exceed 2 wt%, the damping performance of SF @ PUU cement composites weakened.The reason is that the constraint effect of cement interface on PUU weaked with the decrease of interface friction.
In SF cement composites, the particle size of SF is small.When subjected to external excitation load, SF produces relative deformation and friction with surrounding particles and dissipates energy.However, pozzolanic reaction improved the compactness of cement matrix, which generate negative effects on damping properties.In SF@ PUU cement-based composites, the improvement of damping performance is mainly due to interfacial friction energy dissipation between SF@PUU particles and between SF@PUU and cement paste.On the other hand, the PUU coating coated on SF is deformed by SF and cement paste, PUU produces shear strain with vibration.The internal molecular chain of PUU overcomes the internal friction resistance to do work, which dissipates the vibration energy in the form of heat energy, thus causing the energy dissipation of cementbased composites.

Conclusions
In this experiment, a new composite of SF@PUU core-shell particles were proposed, heterogeneous stepwise addition polymerization was used to synthesis SF@PUU core-shell particles, and analyzed the mechanism of the reinforcement effect of SF and SF@PUU on cement composites.Based on its excellent performance, it can be combined with ultrafine cement to prepare grouting vibration damping cementitious composites to reduce the transmission of load to the pavement vibration, which can have a wide range of application prospects in the future in the areas of engineering maintenance, pavement grouting works and repair and reinforcement works.
(1) The damping performance of SF cement composites mainly comes from the relative deformation and friction of particles around SF.The damping properties of SF@PUU cement-based composites can be attributed to interfacial friction and shear energy dissipation of PUU in microscopic constrained damping structure, and it is inferred that interfacial friction energy dissipation may be the main role in SF @ PUU cemen composites.
(2) Realized synchronous improvement of mechanical performance and damping performance.The damping performance of SF@PUU cement composites can be improved by 37%, and the compressive strength of cement composites is 3.5% higher than that of cement paste.
(3) At present, the research was in the initial stage, and the synthesis of core-shell particles was completed in the laboratory.In the next step research, we can design related experimental devices to realize mass production of core-shell particles.On the basis of the research on compressive strength and damping properties of cement composites, we can carry out research on impermeability, durability, corrosion resistance and other related properties.

Figure 2 .
Figure 2. Schematic of experimental setting and specimen dimension vibration test.

Figure 8 .
Figure 8. Compressive strength of 20 mm cube specimens for different FSP and FSP@PUU additions.

Figure 9 .
Figure 9. Vibration waveform for SF cement and SF@PUU cement.

Figure 11 .
Figure 11.Plots of first-order deformation and second-order deformation for ANSYS simulation and EMA simulation (a): first-order deformation plot for ANSYS simulation; b: second-order deformation plot for ANSYS simulation; (c): first-order deformation plot for EMA simulation; (d): second-order deformation plot for EMA simulation).

Table 1 .
Chemical properties of cement.

Table 2 .
SF and SF@PUU cement-based composites modal frequency and damping ratio.